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/icmp_test.go b/ipv4/icmp_test.go
index ce0040d..3324b54 100644
--- a/ipv4/icmp_test.go
+++ b/ipv4/icmp_test.go
@@ -36,7 +36,7 @@
 	switch runtime.GOOS {
 	case "linux":
 	default:
-		t.Skipf("not supported on %q", runtime.GOOS)
+		t.Skipf("not supported on %s", runtime.GOOS)
 	}
 
 	var f ipv4.ICMPFilter
@@ -64,7 +64,7 @@
 	switch runtime.GOOS {
 	case "linux":
 	default:
-		t.Skipf("not supported on %q", runtime.GOOS)
+		t.Skipf("not supported on %s", runtime.GOOS)
 	}
 	if m, ok := nettest.SupportsRawIPSocket(); !ok {
 		t.Skip(m)