MAINTAINERS: add additional maintainer for net/batman-adv

Add myself as maintainer for net/batman-adv as announced by Marek Linder
Signed-off-by: Antonio Quartulli <ordex@autistici.org>

MAINTAINERS

@@ -1431,6 +1431,7 @@ F:	include/linux/backlight.h
 BATMAN ADVANCED
 M:	Marek Lindner <lindner_marek@yahoo.de>
 M:	Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
+M:	Antonio Quartulli <ordex@autistici.org>
 L:	b.a.t.m.a.n@lists.open-mesh.org
 W:	http://www.open-mesh.org/
 S:	Maintained