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>

include/linux/netlink.h

@@ -134,7 +134,7 @@ struct netlink_callback {
 
 struct netlink_notify {
 	struct net *net;
-	int portid;
+	u32 portid;
 	int protocol;
 };