batman-adv: use NO_FLAGS define instead of hard-coding 0

The definition NO_FLAGS was introduced to make the code more
readable and shall be used to initialize flag fields.

Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
diff --git a/net/batman-adv/send.c b/net/batman-adv/send.c
index d0cfa95..a1b8c31 100644
--- a/net/batman-adv/send.c
+++ b/net/batman-adv/send.c
@@ -289,7 +289,7 @@
 		batman_packet->gw_flags =
 				(uint8_t)atomic_read(&bat_priv->gw_bandwidth);
 	else
-		batman_packet->gw_flags = 0;
+		batman_packet->gw_flags = NO_FLAGS;
 
 	atomic_inc(&hard_iface->seqno);