ipv4: remove unnecessary double quotations from test messages

Change-Id: If1243dd2d79824933d896a8c4b31db8c247d0c21
Reviewed-on: https://go-review.googlesource.com/3561
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/ipv4/readwrite_test.go b/ipv4/readwrite_test.go
index e595443..5e6533e 100644
--- a/ipv4/readwrite_test.go
+++ b/ipv4/readwrite_test.go
@@ -91,7 +91,7 @@
 func TestPacketConnConcurrentReadWriteUnicastUDP(t *testing.T) {
 	switch runtime.GOOS {
 	case "nacl", "plan9", "solaris", "windows":
-		t.Skipf("not supported on %q", runtime.GOOS)
+		t.Skipf("not supported on %s", runtime.GOOS)
 	}
 
 	c, err := net.ListenPacket("udp4", "127.0.0.1:0")
@@ -113,7 +113,7 @@
 
 	if err := p.SetControlMessage(cf, true); err != nil { // probe before test
 		if nettest.ProtocolNotSupported(err) {
-			t.Skipf("not supported on %q", runtime.GOOS)
+			t.Skipf("not supported on %s", runtime.GOOS)
 		}
 		t.Fatal(err)
 	}