netlink: Fix portid type in netlink_notify

portid is an unsigned integer. Fix netlink_notify to
match all other portid user in the kernel.

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 02fc86d..6835c12 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -134,7 +134,7 @@
 
 struct netlink_notify {
 	struct net *net;
-	int portid;
+	u32 portid;
 	int protocol;
 };