x/net/ipv4: use new import path for icmp

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/183030043

ipv4/example_test.go

@@ -12,8 +12,8 @@ import (
 	"runtime"
 	"time"
 
+	"golang.org/x/net/icmp"
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/icmp"
 	"golang.org/x/net/ipv4"
 )
 

ipv4/multicast_test.go

@@ -12,8 +12,8 @@ import (
 	"testing"
 	"time"
 
+	"golang.org/x/net/icmp"
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/icmp"
 	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv4"
 )

ipv4/unicast_test.go

@@ -12,8 +12,8 @@ import (
 	"testing"
 	"time"
 
+	"golang.org/x/net/icmp"
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/icmp"
 	"golang.org/x/net/internal/nettest"
 	"golang.org/x/net/ipv4"
 )