mwifiex: configure p2p interface during initialization

Send P2P_MODE_CFG cmd to firmware when p2p interface is created.
Without proper p2p configuration firmware may behave incorrectly
while handling commands sent through this interface.

Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: Stone Piao <piaoyun@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>