batman-adv: convert time_after instances to has_timed_out

To increase readability the has_timed_out() functions has been introduced.
This patch converts existing time_after() calls to use this wrapper
function (if applicable).
This patch also converts all timeouts to miliseconds to be consistent.

Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c
index 24403a7..df5631e 100644
--- a/net/batman-adv/gateway_client.c
+++ b/net/batman-adv/gateway_client.c
@@ -396,7 +396,7 @@
 {
 	struct gw_node *gw_node, *curr_gw;
 	struct hlist_node *node, *node_tmp;
-	unsigned long timeout = 2 * PURGE_TIMEOUT * HZ;
+	unsigned long timeout = msecs_to_jiffies(2 * PURGE_TIMEOUT);
 	int do_deselect = 0;
 
 	curr_gw = gw_get_selected_gw_node(bat_priv);