mwifiex: modify mwifiex_ap_sta_limits to advertise support for P2P

We support maximum simultaneous 2 non-AP station interfaces and
they can assume role of Station/P2P client/P2P GO.
Advertise this support to cfg80211 so that concurrent P2P/STA
operation is possible.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>