batman-adv: fix integer overflow on buff_pos

batman-adv: fix integer overflow on buff_pos

Fixing an integer overflow present in batadv_iv_ogm_send_to_if. The size
check is done using the int type in batadv_iv_ogm_aggr_packet whereas the
buff_pos variable uses the s16 type. This could lead to an out-of-bound
read.

Cc: stable@vger.kernel.org
Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol")
Signed-off-by: Lyes Bourennani <lbourennani@fuzzinglabs.com>
Signed-off-by: Alexis Pinson <apinson@fuzzinglabs.com>
Signed-off-by: Sven Eckelmann <sven@narfation.org>