Add systemd unit files

Being part of the bluetooth.target means that this service (if
enabled) is started automatically every time the bluetooth service is
(re)started.

For WiFi, a NM override is preferred over a sep. systemd service
since bootmac, the driver, and NM seem to race each other. By having
an override for NM that runs bootmac, we can at least guarantee that
bootmac will always run before NM. Other networking daemons could have
similar overrides later.

systemd/bootmac-bluetooth.service

+[Unit]
+Description=Set Bluetooth Mac Address
+PartOf=bluetooth.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/usr/bin/bootmac --bluetooth
+
+[Install]
+WantedBy=bluetooth.target

systemd/bootmac-networkmanager-override.conf

+# Override for NetworkManager.service to run bootmac for WiFi
+[Service]
+ExecStartPre=/usr/bin/bootmac --wlan