wifi: mac80211: isolate driver from inactive links

In order to let the driver select active links and properly
make multi-link connections, as a first step isolate the
driver from inactive links, and set the active links to be
only the association link for client-side interfaces. For
AP side nothing changes since APs always have to have all
their links active.

To simplify things, update the for_each_sta_active_link()
API to include the appropriate vif pointer.

This also implies not allocating a chanctx for an inactive
link, which requires a few more changes.

Since we now no longer try to program multiple links to the
driver, remove the check in the MLME code.

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