wifi: mac80211: expand ieee80211_mgmt_tx() for MLO

There are a couple of new things that should be possible
with MLO:
 * selecting the link to transmit to a station by link ID,
   which a previous patch added to the nl80211 API
 * selecting the link by frequency, similarly
 * allowing transmittion to an MLD without specifying any
   channel or link ID, with MLD addresses

Enable these use cases. Also fix the address comparison
in client mode to use the AP (MLD) address.

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