mac80211: mlme: remove duplicate AID bookkeeping

Maintain the connection AID only in sdata->vif.bss_conf.aid, not
also in sdata->u.mgd.aid.

Keep setting that where we set ifmgd->aid before, which has the
side effect of exposing the AID to the driver before the station
entry (AP) is marked associated, in case it needs it then.

Requested-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Tested-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/20200417123802.085d4a322b0c.I2e7a2ceceea8c6880219f9e9ee4d4ac985fd295a@changeid


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