batman-adv: upgrade package to latest release 2017.4

batman-adv: upgrade package to latest release 2017.4

* support latest kernels (3.2 - 4.15)
* coding style cleanups and refactoring
* documentation cleanup
* bugs squashed:

  - avoid spurious warnings from bat_v neigh_cmp implementation
  - fix check of gateway availability in B.A.T.M.A.N. V
  - fix locking for bidirectional TQ check counters
  - remove leak of stack bits in fragmentation header priority

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