Restart rtirq service after resume from suspend

[terencode]

Fix #3

[terencode]

Because the unit has RemainAfterExit=true it doesn't restart it after the suspend target is reached.
I don't know how to tell systemd to restart the unit after target and not just start which fails because of it's already started.

[terencode]

I found with the help of some folks over at #systemd three ways to do it:

1. Create a new unit file without RemainAfterExit=true that will restart rtirq.service with After=suspend.target
2. Separate the ExecStart and ExecStop into two different units without RemainAfterExit=true.
3. Leave the unit as it is and just put a file in /usr/lib/systemd/system-sleep to call rtirq.service start which will be triggered when receiving the post argument

Which one do you think is better?

[terencode]

@rncbc the PR wasn't ready for merging, you need to tell me which approach you prefer.