batman-adv: update to version 2023.2

* support latest kernels (4.14 - 6.5)
* bugs squashed:
  - avoid potential invalid memory access when processing ELP/OGM2 packets
  - drop pending DAT worker when interface shuts down
  - inform network stack about automatically adjusted MTUs
  - keep user defined MTU limit when MTU is recalculated
  - fix packet memory leak when sending OGM2 via inactive interfaces
  - fix TT memory leak for roamed back clients

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