package/batman-adv: bump to version 2019.3

- Add license files and their hash
- Fix build with latest kernel

This bump should also close
https://bugs.buildroot.org/show_bug.cgi?id=10861



Fixes:
 - No autobuilder failures

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>