x/net/ipv6: use new import path for icmp

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/183040043
diff --git a/ipv6/example_test.go b/ipv6/example_test.go
index 96cbec9..d0c9695 100644
--- a/ipv6/example_test.go
+++ b/ipv6/example_test.go
@@ -11,8 +11,8 @@
 	"os"
 	"time"
 
+	"golang.org/x/net/icmp"
 	"golang.org/x/net/internal/iana"
-	"golang.org/x/net/internal/icmp"
 	"golang.org/x/net/ipv6"
 )
 
diff --git a/ipv6/multicast_test.go b/ipv6/multicast_test.go
index 3c0c5b5..60dea5d 100644
--- a/ipv6/multicast_test.go
+++ b/ipv6/multicast_test.go
@@ -12,8 +12,8 @@
 	"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/ipv6"
 )
diff --git a/ipv6/unicast_test.go b/ipv6/unicast_test.go
index 109c8c6..c4699c1 100644
--- a/ipv6/unicast_test.go
+++ b/ipv6/unicast_test.go
@@ -12,8 +12,8 @@
 	"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/ipv6"
 )