mac80211: make remain_on_channel() op pass vif param

Drivers (e.g. wl12xx) might need to know the vif
to roc on (mainly in order to configure the
rx filters correctly).

Add the vif to the op params, and update the current
users (iwlwifi) to use the new api.

Signed-off-by: Eliad Peller <eliad@wizery.com>
[fix hwsim]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>