go.net/ipv4: make use of internal/{iana,icmp} packages

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/154880043
diff --git a/ipv4/multicastsockopt_test.go b/ipv4/multicastsockopt_test.go
index c476f34..e7d9828 100644
--- a/ipv4/multicastsockopt_test.go
+++ b/ipv4/multicastsockopt_test.go
@@ -5,11 +5,12 @@
 package ipv4_test
 
 import (
-	"code.google.com/p/go.net/ipv4"
 	"net"
 	"os"
 	"runtime"
 	"testing"
+
+	"code.google.com/p/go.net/ipv4"
 )
 
 var packetConnMulticastSocketOptionTests = []struct {