netfilter: nft_socket: remove WARN_ON_ONCE with huge level value

syzbot managed to reach this WARN_ON_ONCE by passing a huge level
value, remove it.

  WARNING: CPU: 0 PID: 5853 at net/netfilter/nft_socket.c:220 nft_socket_init+0x2f4/0x3d0 net/netfilter/nft_socket.c:220

Reported-by: syzbot+a225fea35d7baf8dbdc3@syzkaller.appspotmail.com
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Author: ummakynes

net/netfilter/nft_socket.c

@@ -217,7 +217,7 @@ static int nft_socket_init(const struct nft_ctx *ctx,
 
 		level += err;
 		/* Implies a giant cgroup tree */
-		if (WARN_ON_ONCE(level > 255))
+		if (level > 255)
 			return -EOPNOTSUPP;
 
 		priv->level = level;