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 6b7d163a1e2acc32a05699634084154513377ed1

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