[B.A.T.M.A.N.] mac80211 compat layer for OpenWrt

Hi,

it looks like the next version (with B.A.T.M.A.N. V support and cfg80211 dependency) has to be build against the mac80211 compat version. OpenWrt right now uses Linux 3.18, 4.1, 4.3 and 4.4. These kernel versions don't require many changes (which are not already part of the compat layer) to get batman- adv building against it. But most of the required changes are rather ugly (see batman-adv/patches/0000-compat-hacks.patch). But at least it builds with them.

I have the basic changes for openwrt-routing attached. Maybe someone has some visions how to continue from here.

I've also attached the patch to build the current state of B.A.T.M.A.N. V on OpenWrt.

Kind regards, Sven