wifi: mac80211: fix vif addr when switching from monitor to station

wifi: mac80211: fix vif addr when switching from monitor to station

Since adding support for opting out of virtual monitor support, a zero vif
addr was used to indicate passive vs active monitor to the driver.
This would break the vif->addr when changing the netdev mac address before
switching the interface from monitor to sta mode.
Fix the regression by adding a separate flag to indicate whether vif->addr
is valid.

Reported-by: syzbot+9ea265d998de25ac6a46@syzkaller.appspotmail.com
Fixes: 9d40f7e32774 ("wifi: mac80211: add flag to opt out of virtual monitor support")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://patch.msgid.link/20241115115850.37449-1-nbd@nbd.name
Signed-off-by: Johannes Berg <johannes.berg@intel.com>