mac80211_hwsim: add fake hw scan handler

For debugging hardware scan trigger/complete
functionality, it was useful to have code in
hwsim that pretends to do a hardware scan.

This code could be extended to actually do the
scan, but for now it was sufficient for me to
only pretend. Since hwsim was written to ease
debugging, it only makes sense to add it to it
permanently.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>