Revert "internal/socket: enable {recv,send}mmsg on NetBSD"

This reverts commit 5c0ad186.

Change-Id: I1b6fac0f88816f4464e732d2f8a3d5510decb255
Reviewed-on: https://go-review.googlesource.com/82697Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>

internal/socket/rawconn_mmsg.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build go1.9
-// +build linux netbsd
+// +build linux
 
 package socket
 

internal/socket/rawconn_nommsg.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build go1.9
-// +build !linux,!netbsd
+// +build !linux
 
 package socket
 

internal/socket/socket_go1_9_test.go

@@ -145,7 +145,7 @@ func TestUDP(t *testing.T) {
 		}
 	})
 	switch runtime.GOOS {
-	case "android", "linux", "netbsd":
+	case "android", "linux":
 		t.Run("Messages", func(t *testing.T) {
 			data := []byte("HELLO-R-U-THERE")
 			wmbs := bytes.SplitAfter(data, []byte("-"))
@@ -233,7 +233,7 @@ func BenchmarkUDP(b *testing.B) {
 			}
 		})
 		switch runtime.GOOS {
-		case "android", "linux", "netbsd":
+		case "android", "linux":
 			wms := make([]socket.Message, M)
 			for i := range wms {
 				wms[i].Buffers = [][]byte{data}