wifi: mac80211: pass MBSSID config by reference

It's inefficient and confusing to pass the MBSSID config
by value, requiring the whole struct to be copied. Pass
it by reference instead.

Link: https://patch.msgid.link/20241108092227.48fbd8a00112.I64abc1296a7557aadf798d88db931024486ab3b6@changeid


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