mac80211: upgrade passive scan to active scan on DFS channels after beacon rx

In client mode, we can't connect to hidden SSID APs or SSIDs not advertised
in beacons on DFS channels, since we're forced to passive scan. Fix this by
sending out a probe request immediately after the first beacon, if active
scan was requested by the user.

Cc: stable@vger.kernel.org
Reported-by: Catrinel Catrinescu <cc@80211.de>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20220420104907.36275-1-nbd@nbd.name
Signed-off-by: Johannes Berg <johannes.berg@intel.com>