batman-adv: do_bcast has to be true for broadcast packets only

batman-adv: do_bcast has to be true for broadcast packets only

corrects a critical bug of the GW feature. This bug made all the unicast
packets destined to a GW to be sent as broadcast. This bug is present even if
the sender GW feature is configured as OFF. It's an urgent bug fix and should
be committed as soon as possible.

This was a regression introduced by 56e6c5b46bb6d91a1efb41eee77dd1352416a467

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>