mwifiex: set different mac address for interfaces with same bss type

Multiple interfaces with same bss type could affect each other if
they are sharing the same mac address. In this patch, different
mac address is assigned to new interface which have same bss type
with exist interfaces.

Signed-off-by: Xinming Hu <huxm@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>