netfilter: nft_socket: remove WARN_ON_ONCE on maximum cgroup level

cgroup maximum depth is INT_MAX by default, there is a cgroup toggle to
restrict this maximum depth to a more reasonable value not to harm
performance. Remove unnecessary WARN_ON_ONCE which is reachable from
userspace.

Fixes: 7f3287d ("netfilter: nft_socket: make cgroupsv2 matching work with namespaces")
Reported-by: syzbot+57bac0866ddd99fe47c0@syzkaller.appspotmail.com
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Author: ummakynes

net/netfilter/nft_socket.c

@@ -68,7 +68,7 @@ static noinline int nft_socket_cgroup_subtree_level(void)
 
 	cgroup_put(cgrp);
 
-	if (WARN_ON_ONCE(level > 255))
+	if (level > 255)
 		return -ERANGE;
 
 	if (WARN_ON_ONCE(level < 0))