Staging: batman-adv: send DHCP requests directly to the chosen gw

If the gateway client mode is active batman-adv will send the
broadcasted DHCP requests via unicast to the currently selected best
gateway. Therefore attached clients can profit from batman's knowledge
about the network topology.

Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
[sven.eckelmann@gmx.de: Rework on top of current version]
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>