netfilter: conntrack: Fix UP builds

ARRAY_SIZE(nf_conntrack_locks) is undefined if spinlock_t is an
empty structure. Replace it by CONNTRACK_LOCKS

Fixes: 93bb0ceb75be ("netfilter: conntrack: remove central spinlock nf_conntrack_lock")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netfilter/nf_conntrack_core.c

@@ -1674,7 +1674,7 @@ int nf_conntrack_init_start(void)
 	int max_factor = 8;
 	int i, ret, cpu;
 
-	for (i = 0; i < ARRAY_SIZE(nf_conntrack_locks); i++)
+	for (i = 0; i < CONNTRACK_LOCKS; i++)
 		spin_lock_init(&nf_conntrack_locks[i]);
 
 	/* Idea from tcp.c: use 1/16384 of memory.  On i386: 32MB