hostapd: rework reload support and MAC address handling

hostapd: rework reload support and MAC address handling

MAC address and interface name assigned by mac80211.sh depend on the order in
which interfaces are brought up. This order changes when interfaces get added
or removed, which can cause unnecessary reload churn.

One part of the fix it making MAC address allocation more dynamic in both
wpa_supplicant and hostapd, by ignoring the provided MAC address using
the next available one, whenever the config does not explicitly specify one.

The other part is making use of support for renaming netdevs at runtime and
preserving the MAC address for renamed netdevs.

Signed-off-by: Felix Fietkau <nbd@nbd.name>