Allow configuring different dwell times to the different
scan types (regular and scheduled).

Add new configuration entry (dwell_time_dfs) to
conf_scan_settings, in order to allow setting
different values for normal scan and scheduled scan.
Signed-off-by: NEliad Peller <eliad@wizery.com>
Signed-off-by: NArik Nemtsov <arik@wizery.com>
Signed-off-by: NLuciano Coelho <coelho@ti.com>