[DTV00917783] p2p: Fix crash problem during testing Miracast

[Description]
Fix driver crash problem when disconnecting Miracast connection
from specific phone.

Crash callstack:
Unable to handle kernel NULL pointer dereference at virtual
address 00000008
PC is at mtk_p2p_wext_set_Multicastlist+0x150/0x22c
(mtk_p2p_wext_set_Multicastlist+0x150/0x22c) from (main_thread+0x15c)

when browsing the multicast address list from net_device, we should
check the mc_count before accessing to the ha (netdev_hw_addr *)

Change-Id: Id70c818f7149d6bf75bd5d32972fe415aac36931
Signed-off-by: Sarick Jiang <sarick.jiang@mediatek.com>
CR-Id: DTV00917783
Feature: p2p
Reviewed-on: http://gerrit.mediatek.inc:8080/1250569
CheckPatch: Check Patch <srv_checkpatch@mediatek.com>
Reviewed-by: George Kuo <george.kuo@mediatek.com>
(cherry picked from commit b4ed3895dbc7667bbbf89d62c29aff02da6fca08)
Reviewed-on: http://gerrit.mediatek.inc:8080/1267238
Reviewed-by: Wayne Guo <wayne.guo@mediatek.com>
Build: srv_neptune_adm <srv_neptune_adm@mediatek.com>
1 file changed