mwifiex: common set_wiphy_params cfg80211 handler for AP and STA interface

Add support for setting fragmentation threshold, RTS threshold
and retry limit.
Since wiphy parameters are properties of physical device,
appropriate function to set phy parameters is invoked depending
upon bss_type(STA or AP) for each virtual interface.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: Kiran Divekar <dkiran@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>