util/deephash: don't reflect.Copy if element type is a defined uint8

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

util/deephash/deephash.go

@@ -125,6 +125,8 @@ func (h *hasher) int(i int) {
 	h.bw.Write(h.scratch[:8])
 }
 
+var uint8Type = reflect.TypeOf(byte(0))
+
 // print hashes v into w.
 // It reports whether it was able to do so without hitting a cycle.
 func (h *hasher) print(v reflect.Value) (acyclic bool) {
@@ -172,7 +174,7 @@ func (h *hasher) print(v reflect.Value) (acyclic bool) {
 		if v.Kind() == reflect.Slice {
 			h.int(vLen)
 		}
-		if v.Type().Elem().Kind() == reflect.Uint8 && v.CanInterface() {
+		if v.Type().Elem() == uint8Type && v.CanInterface() {
 			if vLen > 0 && vLen <= scratchSize {
 				// If it fits in scratch, avoid the Interface allocation.
 				// It seems tempting to do this for all sizes, doing

util/deephash/deephash_test.go

@@ -15,8 +15,10 @@ import (
 
 	"inet.af/netaddr"
 	"tailscale.com/tailcfg"
+	"tailscale.com/types/ipproto"
 	"tailscale.com/util/dnsname"
 	"tailscale.com/version"
+	"tailscale.com/wgengine/filter"
 	"tailscale.com/wgengine/router"
 	"tailscale.com/wgengine/wgcfg"
 )
@@ -126,6 +128,9 @@ func getVal() []interface{} {
 				{ID: 2, LoginName: "bar@foo.com"},
 			},
 		},
+		filter.Match{
+			IPProto: []ipproto.Proto{1, 2, 3},
+		},
 	}
 }