batman-adv: update to current openwrt-routing / batman-adv v2019.2

This updates the batman-adv OpenWrt package to the current version
provided in the master branch of the openwrt-routing packages
repository:

* e26096a batman-adv: Fix duplicated OGMs on NETDEV_UP
* 1ff00ee batman-adv: upgrade package to latest release 2019.2

Small difference to the original:

* Compat code for batadv_genl_dump_check_consistent()
* Compat code for cfg80211_sinfo_release_content()
* 0001-batman-adv-add-compat-hacks.patch kept
* batctl dependency kept removed
* config related files unchanged

The new config format was not backported yet to keep this patch small
and less invasive.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>