ipv4: make use of nettest.SupportsRawIPSocket

Change-Id: I12b41d16b49415081242e06b25a7106a4a0c0442
Reviewed-on: https://go-review.googlesource.com/3402
Reviewed-by: Ian Lance Taylor <iant@golang.org>

ipv4/multicastlistener_test.go

diff --git a/ipv4/multicastlistener_test.go b/ipv4/multicastlistener_test.go
index f9d7791..fd6dd75 100644
--- a/ipv4/multicastlistener_test.go
+++ b/ipv4/multicastlistener_test.go
@@ -6,7 +6,6 @@
 
 import (
 	"net"
-	"os"
 	"runtime"
 	"testing"
 
@@ -163,8 +162,8 @@
 	if testing.Short() {
 		t.Skip("to avoid external network")
 	}
-	if os.Getuid() != 0 {
-		t.Skip("must be root")
+	if m, ok := nettest.SupportsRawIPSocket(); !ok {
+		t.Skip(m)
 	}
 
 	c, err := net.ListenPacket("ip4:icmp", "0.0.0.0") // wildcard address
@@ -208,8 +207,8 @@
 	if testing.Short() {
 		t.Skip("to avoid external network")
 	}
-	if os.Getuid() != 0 {
-		t.Skip("must be root")
+	if m, ok := nettest.SupportsRawIPSocket(); !ok {
+		t.Skip(m)
 	}
 
 	gaddr := net.IPAddr{IP: net.IPv4(224, 0, 0, 254)} // see RFC 4727