net/memnet: export the network name (#9111)

This makes it more maintainable for other code to statically depend
on the exact value of this string. It also makes it easier to
identify what code might depend on this string by looking up
references to this constant.

Updates tailscale/corp#13777

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

net/memnet/conn.go

@@ -9,6 +9,10 @@ import (
 	"time"
 )
 
+// NetworkName is the network name returned by [net.Addr.Network]
+// for [net.Conn.LocalAddr] and [net.Conn.RemoteAddr] from the [Conn] type.
+const NetworkName = "mem"
+
 // Conn is a net.Conn that can additionally have its reads and writes blocked and unblocked.
 type Conn interface {
 	net.Conn
@@ -45,7 +49,7 @@ func NewTCPConn(src, dst netip.AddrPort, maxBuf int) (local Conn, remote Conn) {
 
 type connAddr string
 
-func (a connAddr) Network() string { return "mem" }
+func (a connAddr) Network() string { return NetworkName }
 func (a connAddr) String() string  { return string(a) }
 
 type connHalf struct {