iwlwifi: Logic to control how frequent radio should be reset if needed

Add additional logic for internal scan routine to control how
frequent this function should be performed.

The intent of this function is to reset/re-tune the radio and bring the
RF/PHY back to normal state, it does not make sense calling it too
frequent,
if reset the radio can not bring it back to normal state, it indicate
there are other reason to cause the radio not operate correctly.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>