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

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/167030043
diff --git a/ipv6/sys_bsd.go b/ipv6/sys_bsd.go
index 36039ac..cc5bc5c 100644
--- a/ipv6/sys_bsd.go
+++ b/ipv6/sys_bsd.go
@@ -10,7 +10,7 @@
 	"net"
 	"syscall"
 
-	"code.google.com/p/go.net/internal/iana"
+	"golang.org/x/net/internal/iana"
 )
 
 type sysSockoptLen int32