[NETFILTER] ctnetlink: add module alias to fix autoloading

Add missing module alias. This is a must to load ctnetlink on demand. For
example, the conntrack tool will fail if the module isn't loaded.
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: NHarald Welte <laforge@netfilter.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/netfilter/ip_conntrack_netlink.c

@@ -1538,6 +1538,8 @@ static struct nfnetlink_subsystem ctnl_exp_subsys = {
 	.cb				= ctnl_exp_cb,
 };
 
+MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_CTNETLINK);
+
 static int __init ctnetlink_init(void)
 {
 	int ret;