wifi: Update active iface when bridged AP instance down

The active interface need to be updated when any of interface changecd.

Also fix the local cache bridged_ap_instances value incorrect
when erasing.

Bug: 191625124
Test: Manual check property "wifi.active.interface" after wlan2 down
Test: Manual test with command "halutil -sar enable 0" after wlan2 down
Change-Id: I40150c231313505ca355228e711c2448088f41ad