go.net: use golang.org/x/... import paths

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/167030043
diff --git a/ipv4/multicastsockopt_test.go b/ipv4/multicastsockopt_test.go
index d9fa7f0..cda97bd 100644
--- a/ipv4/multicastsockopt_test.go
+++ b/ipv4/multicastsockopt_test.go
@@ -10,8 +10,8 @@
 	"runtime"
 	"testing"
 
-	"code.google.com/p/go.net/internal/nettest"
-	"code.google.com/p/go.net/ipv4"
+	"golang.org/x/net/internal/nettest"
+	"golang.org/x/net/ipv4"
 )
 
 var packetConnMulticastSocketOptionTests = []struct {