wifi: mac80211: fix control port frame addressing

For an AP interface, when userspace specifieds the link ID to
transmit the control port frame on (in particular for the
initial 4-way-HS), due to the logic in ieee80211_build_hdr()
for a frame transmitted from/to an MLD, we currently build a
header with

 A1 = DA = MLD address of the peer MLD
 A2 = local link address (!)
 A3 = SA = local MLD address

This clearly makes no sense, and leads to two problems:
 - if the frame were encrypted (not true for the initial
   4-way-HS) the AAD would be calculated incorrectly
 - if iTXQs are used, the frame is dropped by logic in
   ieee80211_tx_dequeue()

Fix the addressing, which fixes the first bullet, and the
second bullet for peer MLDs, I'll fix the second one for
non-MLD peers separately.

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