MINOR: server: replace the pendconns-related stuff with a struct queue

Just like for proxies, all three elements (pendconns, nbpend, queue_idx)
were moved to struct queue.
diff --git a/src/lb_map.c b/src/lb_map.c
index b735678..592df91 100644
--- a/src/lb_map.c
+++ b/src/lb_map.c
@@ -230,7 +230,7 @@
 	avoididx = 0; /* shut a gcc warning */
 	do {
 		srv = px->lbprm.map.srv[newidx++];
-		if (!srv->maxconn || (!srv->nbpend && srv->served < srv_dynamic_maxconn(srv))) {
+		if (!srv->maxconn || (!srv->queue.length && srv->served < srv_dynamic_maxconn(srv))) {
 			/* make sure it is not the server we are try to exclude... */
 			/* ...but remember that is was selected yet avoided */
 			avoided = srv;