hostapd: Make inactivity polling configurable

hostapd: Make inactivity polling configurable

hostapd uses the poll method to check if the station is alive
after the station has been inactive for ap_max_inactivity seconds.
Make the poll mechanism configurable so that user can choose to
disconnect idle clients.

This can be especially useful when some devices/firmwares have
restrictions on the number of clients that can connect to the AP
and that limit is smaller than the total number of stations trying
to use the AP.

Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: Nishant Sarmukadam <nishants@marvell.com>