[B.A.T.M.A.N.] batman-adv gateway support

[Marek Lindner <lindner_marek@yahoo.de>]

Hi,

batman-adv still lacks the well-known gateway functionality the batman daemon 
offered since quite a while. Since batman-adv works sufficiently well without it 
and due to the ongoing debate whether a layer 2 mesh protocol should interfere 
with layer 3 this topic has been neglected for a while. In multi-gateway 
environments proper gateway support is a must have. Therefore I hereby propose 
a set of patches to add this functionality. Comments welcome!

What you get:
* The first patch will add gateway announce / handling support to the protocol. 
You will have additional /proc files to switch gateway modes, get a list of 
gateways in the network and see the currently selected best gateway. 
* The second patch simply adds batctl support to conveniently configure the 
gateway setup.
* The third patch checks whether locally received packets are DHCP queries and 
forwards them via uncicast to the best gateway instead of broadcasting them.

Note:
* These patches change the routing protocol, therefore the compat version is 
increased. This (intentionally) breaks interoperability with older batman-adv 
versions!
* Only DHCP traffic gets redirected to the best gateway - no other traffic is 
affected. This is part of the compromise we achieved during the last 
discussions.
* IPv6 support is still missing but should be fairly easy to add. Any 
volunteers ?

Regards,
Marek