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

net/wireless/rdev-ops.h

@@ -538,6 +538,10 @@ static inline int
 rdev_set_wiphy_params(struct cfg80211_registered_device *rdev, u32 changed)
 {
 	int ret;
+
+	if (!rdev->ops->set_wiphy_params)
+		return -EOPNOTSUPP;
+
 	trace_rdev_set_wiphy_params(&rdev->wiphy, changed);
 	ret = rdev->ops->set_wiphy_params(&rdev->wiphy, changed);
 	trace_rdev_return_int(&rdev->wiphy, ret);