netfilter: nat: use test_and_clear_bit when deleting ct from bysource list

We can use a single statement for this.
While at it, fixup the comment -- we don't have pernet table/ops
anymore, the function is only called from module exit path.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_nat_core.c

@@ -542,17 +542,14 @@ static int nf_nat_proto_clean(struct nf_conn *ct, void *data)
 	if (nf_nat_proto_remove(ct, data))
 		return 1;
 
-	if ((ct->status & IPS_SRC_NAT_DONE) == 0)
-		return 0;
-
-	/* This netns is being destroyed, and conntrack has nat null binding.
+	/* This module is being removed and conntrack has nat null binding.
 	 * Remove it from bysource hash, as the table will be freed soon.
 	 *
 	 * Else, when the conntrack is destoyed, nf_nat_cleanup_conntrack()
 	 * will delete entry from already-freed table.
 	 */
-	clear_bit(IPS_SRC_NAT_DONE_BIT, &ct->status);
-	__nf_nat_cleanup_conntrack(ct);
+	if (test_and_clear_bit(IPS_SRC_NAT_DONE_BIT, &ct->status))
+		__nf_nat_cleanup_conntrack(ct);
 
 	/* don't delete conntrack.  Although that would make things a lot
 	 * simpler, we'd end up flushing all conntracks on nat rmmod.