BUG/MINOR: log: release global log servers on exit

Since 2.6 we have a free_logsrv() function that is used to release log
servers. It must be called from deinit() instead of manually iterating
over the log servers, otherwise some parts of the structure are not
freed (namely the ring name), as reported by ASAN.

This should be backported to 2.6.
diff --git a/src/haproxy.c b/src/haproxy.c
index e0b48a7..3cf57e4 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -2823,10 +2823,10 @@
 	idle_conn_task = NULL;
 
 	list_for_each_entry_safe(log, logb, &global.logsrvs, list) {
-			LIST_DELETE(&log->list);
-			free(log->conf.file);
-			free(log);
-		}
+		LIST_DEL_INIT(&log->list);
+		free_logsrv(log);
+	}
+
 	list_for_each_entry_safe(wl, wlb, &cfg_cfgfiles, list) {
 		free(wl->s);
 		LIST_DELETE(&wl->list);