mwifiex: set channel via start_ap handler for AP interface

This patch adds functionality to set channel info received from
cfg80211_ap_settings in start_ap handler.

Since set_channel cfg80211 handler has been removed and we need
not explicitely call mwifiex_uap_set_channel(); hence this
function definition is also removed.

Signed-off-by: Avinash Patil <patila@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>