wgengine/router/dns: remove unsafe endianness detection on Linux

cmd/tailscale/depaware.txt

@@ -71,7 +71,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/types/opt                                      from tailscale.com/control/controlclient+
         tailscale.com/types/strbuilder                               from tailscale.com/net/packet
         tailscale.com/types/structs                                  from tailscale.com/control/controlclient+
-   W    tailscale.com/util/endian                                    from tailscale.com/net/netns
+  LW    tailscale.com/util/endian                                    from tailscale.com/net/netns+
         tailscale.com/util/lineread                                  from tailscale.com/control/controlclient+
         tailscale.com/util/systemd                                   from tailscale.com/control/controlclient+
         tailscale.com/version                                        from tailscale.com/cmd/tailscale/cli+
@@ -81,7 +81,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/wgengine/magicsock                             from tailscale.com/wgengine
      💣 tailscale.com/wgengine/monitor                               from tailscale.com/cmd/tailscale/cli+
         tailscale.com/wgengine/router                                from tailscale.com/cmd/tailscale/cli+
-     💣 tailscale.com/wgengine/router/dns                            from tailscale.com/ipn+
+        tailscale.com/wgengine/router/dns                            from tailscale.com/ipn+
         tailscale.com/wgengine/tsdns                                 from tailscale.com/ipn+
         tailscale.com/wgengine/tstun                                 from tailscale.com/wgengine
    W 💣 tailscale.com/wgengine/winnet                                from tailscale.com/wgengine/router

cmd/tailscaled/depaware.txt

@@ -79,7 +79,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/types/opt                                      from tailscale.com/control/controlclient+
         tailscale.com/types/strbuilder                               from tailscale.com/net/packet
         tailscale.com/types/structs                                  from tailscale.com/control/controlclient+
-   W    tailscale.com/util/endian                                    from tailscale.com/net/netns+
+  LW    tailscale.com/util/endian                                    from tailscale.com/net/netns+
         tailscale.com/util/lineread                                  from tailscale.com/control/controlclient+
         tailscale.com/util/pidowner                                  from tailscale.com/ipn/ipnserver
         tailscale.com/util/racebuild                                 from tailscale.com/logpolicy
@@ -91,7 +91,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/wgengine/magicsock                             from tailscale.com/cmd/tailscaled+
      💣 tailscale.com/wgengine/monitor                               from tailscale.com/wgengine
         tailscale.com/wgengine/router                                from tailscale.com/cmd/tailscaled+
-     💣 tailscale.com/wgengine/router/dns                            from tailscale.com/ipn+
+        tailscale.com/wgengine/router/dns                            from tailscale.com/ipn+
         tailscale.com/wgengine/tsdns                                 from tailscale.com/ipn+
         tailscale.com/wgengine/tstun                                 from tailscale.com/wgengine
    W 💣 tailscale.com/wgengine/winnet                                from tailscale.com/wgengine/router

wgengine/router/dns/nm.go

@@ -10,30 +10,14 @@ import (
 	"bufio"
 	"bytes"
 	"context"
-	"encoding/binary"
 	"fmt"
 	"os"
 	"os/exec"
-	"unsafe"
 
 	"github.com/godbus/dbus/v5"
+	"tailscale.com/util/endian"
 )
 
-var nativeEndian binary.ByteOrder
-
-func init() {
-	// TODO(dmytro): use DBus endianness flag when available.
-	// A more elegant way to do this is by looking at the first byte of a raw DBus message.
-	// However, that requires a change in godbus, which has slow maintainer response.
-	i := uint32(1)
-	p := unsafe.Pointer(&i)
-	if *(*byte)(p) == 1 {
-		nativeEndian = binary.LittleEndian
-	} else {
-		nativeEndian = binary.BigEndian
-	}
-}
-
 // isNMActive determines if NetworkManager is currently managing system DNS settings.
 func isNMActive() bool {
 	// This is somewhat tricky because NetworkManager supports a number
@@ -145,7 +129,7 @@ func (m nmManager) Up(config Config) error {
 	for _, ip := range config.Nameservers {
 		b := ip.As16()
 		if ip.Is4() {
-			dnsv4 = append(dnsv4, nativeEndian.Uint32(b[12:]))
+			dnsv4 = append(dnsv4, endian.Native.Uint32(b[12:]))
 		} else {
 			dnsv6 = append(dnsv6, b[:])
 		}