net: add BenchmarkReadWriteMsgUDPAddrPort

The main item of interest here is the allocs.

BenchmarkReadWriteMsgUDPAddrPort-8   	  195920	      6450 ns/op	     176 B/op	       5 allocs/op

Change-Id: I358bd18888ce254b6c6d5d5c920e6d22ce5a2ef4
Reviewed-on: https://go-review.googlesource.com/c/go/+/360595
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/udpsock_test.go

@@ -474,6 +474,27 @@ func TestUDPReadTimeout(t *testing.T) {
 	}
 }
 
+func BenchmarkReadWriteMsgUDPAddrPort(b *testing.B) {
+	conn, err := ListenUDP("udp4", &UDPAddr{IP: IPv4(127, 0, 0, 1)})
+	if err != nil {
+		b.Fatal(err)
+	}
+	addr := conn.LocalAddr().(*UDPAddr).AddrPort()
+	buf := make([]byte, 8)
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		_, _, err := conn.WriteMsgUDPAddrPort(buf, nil, addr)
+		if err != nil {
+			b.Fatal(err)
+		}
+		_, _, _, _, err = conn.ReadMsgUDPAddrPort(buf, nil)
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
 func BenchmarkWriteToReadFromUDP(b *testing.B) {
 	conn, err := ListenUDP("udp4", &UDPAddr{IP: IPv4(127, 0, 0, 1)})
 	if err != nil {