nl80211: Avoid AP mode BUG_ON hang with invalid lock assert

"cfg80211: add assert_cfg80211_lock() to ensure proper protection"
added assert_cfg80211_lock() calls into various places. At least
one of them, nl80211_send_wiphy(), should not have been there. That
triggers the BUG_ON in assert_cfg80211_lock() and pretty much kills
the kernel whenever someone runs hostapd.. Remove that call and make
assert_cfg80211_lock() use WARN_ON instead of BUG_ON to be a bit more
friendly to users.

Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>