Staging: batman-adv: register the batman-adv packet type per interface

Batman-adv globally registered the batman-adv packet type and installed
a hook to batman_skb_recv(). Each interface receiving a packet with that
type would end up in this function which then had to loop through all
batman-adv internal interface structures to find the its meta data. The
more interfaces a system had the longer the loops might take. Each and
every packet goes through this function making it a performance critical
loop.

This patch installs the hook for each activated interface. The called
batman_skb_recv() can distinguish these calls, therefore avoiding the
loop through the interface structures.

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>