mwifiex: bring in scan channel gap feature

With scan channel gap when any station/AP is active, FW comes back
to connected channel for any pending data transfter after scanning each
channel.
We set scan channel gap TLV to FW in scan command when any of the
interface is active. This enables scan channel gap in FW.
Also when scan channel gap is enabled, we would scan maximum channels
allowed by FW.

Scan channel gap is supported only on FW with V15 FW API.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Marc Yang <yangyang@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>