batman-adv: add kerneldoc for dst_hint argument

Some helper functions used along the TX path have now a new
"dst_hint" argument but the kerneldoc was missing.

Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
diff --git a/net/batman-adv/send.c b/net/batman-adv/send.c
index 0e4831f..ce163d5 100644
--- a/net/batman-adv/send.c
+++ b/net/batman-adv/send.c
@@ -311,6 +311,7 @@
  * @packet_type: the batman unicast packet type to use
  * @packet_subtype: the unicast 4addr packet subtype (only relevant for unicast
  *  4addr packets)
+ * @dst_hint: can be used to override the destination contained in the skb
  * @vid: the vid to be used to search the translation table
  *
  * Look up the recipient node for the destination address in the ethernet