[X13s] Set unique bluetooth mac address

On windows side MAC address for WLAN and Bluetooth are similar - like off by 4 from each other. I am guessing that a range of MACs is used per device (i.e. sequentially for wlan, sim cards, bluetooth).

On linux side we do not currently have ability to find out the expected device MAC.

Currently setting to static one is ok, but will not work when all of us are in Riga with all of our X13s devices.

[Unit]
Description=Set Bluetooth Address
After=bluetooth.target
Requires=bluetooth.target

[Service]
Type=simple
ExecStartPre=/usr/bin/sleep 5
ExecStart=/bin/bash -c "/usr/bin/yes | /usr/bin/btmgmt public-addr AD:5A:00:F0:FD:8C"

[Install]
WantedBy=multi-user.target

Imho this should be impoved as follows:

1) make this wantedby individual bluetooth device, not bluetooth.target
2) make it bind to bluetooth device, such that it is stopped/started upon device poweroff/poweron (need to check if needed to set address every time)
3) make it conditional on btmgmt to be available
4) set or derive MAC from /etc/machine-id (maybe systemd should be able to do this for us?)
5) use btmgmt --timeout option for interactive use
6) Hopefully above will mean there is no need to do sleep 5 either