Speedy join only works when the received packet is either broadcast or an
4addr unicast packet. Thus packets converted from broadcast to unicast via
the gateway handling code have to be converted to 4addr packets to allow
the receiving gateway server to add the sender address as temporary entry
to the translation table.

Not doing it will make the batman-adv gateway server drop the DHCP response
in many situations because it doesn't yet have the TT entry for the
destination of the DHCP response.

Signed-off-by: Sven Eckelmann <sven@narfation.org>

batman-adv & alfred 2016.2.

Should be redundant after 0bd0df6f

This also updates batman-adv & alfred to 2015.1

This should workaround batman-adv's inability to deal with different MTUs
which need fragmentation.

Fixes #435

This gets us an up-to-date alfred (and batman-adv 2014.x, as soon as we start to
support it).