netfilter: nfnetlink: don't probe module if it exists

commit dbc3617f upstream.

nfnetlink_bind request_module()s all the time as nfnetlink_get_subsys()
shifts the argument by 8 to obtain the subsys id.

So using type instead of type << 8 always returns NULL.

Fixes: 03292745 ("netlink: add nlk->netlink_bind hook for module auto-loading")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

net/netfilter/nfnetlink.c

@@ -406,7 +406,7 @@ static int nfnetlink_bind(int group)
 	int type = nfnl_group2type[group];
 
 	rcu_read_lock();
-	ss = nfnetlink_get_subsys(type);
+	ss = nfnetlink_get_subsys(type << 8);
 	rcu_read_unlock();
 	if (!ss)
 		request_module("nfnetlink-subsys-%d", type);