cfg80211: check for set_wiphy_params

Check if set_wiphy_params is assigned and return an error if not,
some drivers (e.g. virt_wifi where syzbot reported it) don't have
it.

Reported-by:  <syzbot+e8a797964a4180eb57d5@syzkaller.appspotmail.com>
Reported-by:  <syzbot+34b582cf32c1db008f8e@syzkaller.appspotmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20200113125358.ac07f276efff.Ibd85ee1b12e47b9efb00a2adc5cd3fac50da791a@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>