MINOR: server: return the next srv instance on free_server

As a convenience, return the next server instance from servers list on
free_server.

This is particularily useful when using this function on the servers
list without having to save of the next pointer before calling it.

(cherry picked from commit f5c1e12e44e1caa0185e063daf00fb8841c2ed3d)
[ad: updated context: remove uneeded condition on srv]
Signed-off-by: Amaury Denoyelle <adenoyelle@haproxy.com>
diff --git a/src/proxy.c b/src/proxy.c
index 0e96571..54aaa8d 100644
--- a/src/proxy.c
+++ b/src/proxy.c
@@ -131,7 +131,7 @@
 
 void free_proxy(struct proxy *p)
 {
-	struct server *s,*s_next;
+	struct server *s;
 	struct cap_hdr *h,*h_next;
 	struct listener *l,*l_next;
 	struct bind_conf *bind_conf, *bind_back;
@@ -286,11 +286,9 @@
 
 	s = p->srv;
 	while (s) {
-		s_next = s->next;
 		list_for_each_entry(srvdf, &server_deinit_list, list)
 			srvdf->fct(s);
-		free_server(s);
-		s = s_next;
+		s = free_server(s);
 	}/* end while(s) */
 
 	list_for_each_entry_safe(l, l_next, &p->conf.listeners, by_fe) {