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/multicastlistener_test.go b/ipv4/multicastlistener_test.go
index 8b1863f..0578b37 100644
--- a/ipv4/multicastlistener_test.go
+++ b/ipv4/multicastlistener_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 udpMultipleGroupListenerTests = []net.Addr{
@@ -23,7 +24,7 @@
 	case "plan9", "windows":
 		t.Skipf("not supported on %q", runtime.GOOS)
 	}
-	if testing.Short() || !*testExternal {
+	if testing.Short() {
 		t.Skip("to avoid external network")
 	}
 
@@ -63,7 +64,7 @@
 	case "plan9", "windows":
 		t.Skipf("not supported on %q", runtime.GOOS)
 	}
-	if testing.Short() || !*testExternal {
+	if testing.Short() {
 		t.Skip("to avoid external network")
 	}
 
@@ -115,7 +116,7 @@
 	case "plan9", "windows":
 		t.Skipf("not supported on %q", runtime.GOOS)
 	}
-	if testing.Short() || !*testExternal {
+	if testing.Short() {
 		t.Skip("to avoid external network")
 	}
 
@@ -158,7 +159,7 @@
 	case "plan9", "windows":
 		t.Skipf("not supported on %q", runtime.GOOS)
 	}
-	if testing.Short() || !*testExternal {
+	if testing.Short() {
 		t.Skip("to avoid external network")
 	}
 	if os.Getuid() != 0 {
@@ -203,7 +204,7 @@
 	case "plan9", "windows":
 		t.Skipf("not supported on %q", runtime.GOOS)
 	}
-	if testing.Short() || !*testExternal {
+	if testing.Short() {
 		t.Skip("to avoid external network")
 	}
 	if os.Getuid() != 0 {