BUILD: listener: avoir a build warning when threads are disabled

It's just a __decl_thread() that appeared before the last variable.
diff --git a/src/listener.c b/src/listener.c
index 320fc5e..85191f5 100644
--- a/src/listener.c
+++ b/src/listener.c
@@ -762,8 +762,8 @@
 	 */
 	for (; max_accept; next_conn = next_feconn = next_actconn = 0, max_accept--) {
 		unsigned int count;
-		__decl_thread(unsigned long mask);
 		int status;
+		__decl_thread(unsigned long mask);
 
 		/* pre-increase the number of connections without going too far.
 		 * We process the listener, then the proxy, then the process.