Add batman-adv patch to remove gw mode switch message

This patch suppresses the messages batman writes to
the kernel log when gw_mode is changed. This is done
to avoid spamming the log with negligible messages
when gw_mode is switched frequently.

Fixes: #93

Signed-off-by: Fabian Bläse <fabian@blaese.de>
Reviewed-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Robert Langhammer <rlanghammer@web.de>
Reviewed-by: Tim Niemeyer <tim@tn-x.org>
Tested-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>