All batman-adv packets have a common 3 byte header. It can be used to share
some code between different code paths, but it was never explicit stated that
this header has to be always the same for all packets. Therefore, new code
changes always have the problem that they may accidently introduce regressions
by moving some elements around.

A new structure is introduced that contains the common header and makes it
easier visible that these 3 bytes have to be the same for all on-wire packets.
Signed-off-by: NSven Eckelmann <sven@narfation.org>
Signed-off-by: NMarek Lindner <lindner_marek@yahoo.de>

In the process the batman iv OGM aggregation code could be merged
into the batman iv code base which makes the separate aggregation
files superfluous.
Signed-off-by: NMarek Lindner <lindner_marek@yahoo.de>

Signed-off-by: NMarek Lindner <lindner_marek@yahoo.de>

In preparation of the upcoming improved routing algorithm the code based has
to be re-organized to allow choosing the routing algorithm at compile time.
Signed-off-by: NMarek Lindner <lindner_marek@yahoo.de>