batman-adv: upgrade package to latest release 2018.2

batman-adv: upgrade package to latest release 2018.2

* support latest kernels (3.16 - 4.18)
* dropped support for kernels < 3.16 (note the removed build directory)
* coding style cleanups and refactoring
* avoid old nodes disabling multicast optimizations completely
* disable ethtool based B.A.T.M.A.N. V speed detection for virtual interfaces
* enable B.A.T.M.A.N. V compilation by default
* disable debugfs support by default
* bugs squashed:

  - fix TT sync flags for intermediate TT responses
  - avoid race in TT TVLV allocator helper
  - prevent TT request storms by not sending inconsistent TT TVLVs
  - fix best gw refcnt after netlink dump
  - adjust debugfs paths for interfaces after a namechange
  - fix single entry TT non-sync flag storage
  - fix multicast TT issues with bogus ROAM flags
  - work around insufficient memory initialization in cfg80211's station info

Signed-off-by: Sven Eckelmann <sven@narfation.org>