netfilter: nfnetlink_queue: Initialize ctx to avoid memory allocation error

It is possible that ctx in nfqnl_build_packet_message() could be used
before it is properly initialize, which is only initialized
by nfqnl_get_sk_secctx().

This patch corrects this problem by initializing the lsmctx to a safe
value when it is declared.

This is similar to the commit 35fcac7a7c25
("audit: Initialize lsmctx to avoid memory allocation error").

Fixes: 2d470c778120 ("lsm: replace context+len with lsm_context")
Signed-off-by: Chenyuan Yang <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nfnetlink_queue.c

···
 	enum ip_conntrack_info ctinfo = 0;
 	const struct nfnl_ct_hook *nfnl_ct;
 	bool csum_verify;
-	struct lsm_context ctx;
+	struct lsm_context ctx = { NULL, 0, 0 };
 	int seclen = 0;
 	ktime_t tstamp;