BUG/MEDIUM: init/threads: consider epoll_fd/pipes for automatic maxconn calculation

This is the equivalent of the previous patch for the automatic maxconn
calculation. This doesn't need any backport.
diff --git a/src/haproxy.c b/src/haproxy.c
index b7979ea..28c72a5 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -1478,6 +1478,12 @@
 	/* subtract listeners and checks */
 	remain -= global.maxsock;
 
+	/* one epoll_fd/kqueue_fd per thread */
+	remain -= global.nbthread;
+
+	/* one wake-up pipe (2 fd) per thread */
+	remain -= 2 * global.nbthread;
+
 	/* Fixed pipes values : we only subtract them if they're not larger
 	 * than the remaining FDs because pipes are optional.
 	 */