main/bootmac: support systemd

This new version includes initial support for systemd (for bluetooth only atm). udev rules are only installed for openrc systems, bt config on systemd was replaced by a unit file and using bootmac for wifi has issues (bootmac#7)

old description

This adds a -systemd subpkg to install a unit file (for bluetooth right now). This also includes some patches that were sent upstream to bootmac project, which can be dropped if/when it's accepted in the bootmac project and a new release is made.

The patches here have been sent upstream: bootmac!10 (merged)

openrc installs will still use the udev rule to run bootmac for bluetooth, since that seems to work reliably (and there's no concept of service targets or anything that would make this easy to implement on openrc, but I digress).

Both systemd and openrc installs will continue to use udev rules for wifi mac setting, I don't have a way to test that this works, sd unit file can be created later if it improves the situation there.

cc @DylanVanAssche