olsrd: add ubus ipc integration to olsrd

olsrd: add ubus ipc integration to olsrd

IPC integration of olsrd with OpenWrt. Allow dynamic adding and removing
of interfaces at run-time. We need to rename the avl-tree files, since
libubox also defines avl tree. Also add patch to allow meshing via
wireguard point-to-point links.

The ubus interface offers following functions:
  - add_inteface '{"ifname":"wg_51820"}'
  - del_inteface '{"ifname":"wg_51820"}'

Signed-off-by: Nick Hainke <vincent@systemli.org>
(cherry picked from commit 0bffe620b441c039780d4336a15c8ed4f2ebbbf4)