wifi: mac80211: add pointer from bss_conf to vif

wifi: mac80211: add pointer from bss_conf to vif

While often not needed, this considerably simplifies going from a link
specific bss_config to the vif. This helps with e.g. creating link
specific debugfs entries inside drivers.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230301115906.46f701a10ed5.I20390b2a8165ff222d66585915689206ea93222b@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>