wifi: mac80211: replace link_id with link_conf in switch/(un)assign_vif_chanctx()

Since mac80211 already has a protected pointer to link_conf,
pass it to the driver to avoid additional RCU locking.

Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>