test: reset systemd-udevd.service restart counter

test: reset systemd-udevd.service restart counter

Since we restart systemd-udevd here a couple of times, we might hit the
rate limit in later tests:

[   26.028355] testsuite-17.sh[2074]: + udevadm control -e
[   26.028355] testsuite-17.sh[2074]: + udevadm control -l emerg
[   26.126160] systemd[1]: systemd-udevd.service: Start request repeated too quickly.
[   26.126213] systemd[1]: systemd-udevd.service: Failed with result 'start-limit-hit'.
[   26.140310] systemd[1]: Failed to start systemd-udevd.service.
[   26.140897] systemd[1]: systemd-udevd-control.socket: Failed with result 'service-start-limit-hit'.
[   26.141286] systemd[1]: systemd-udevd-kernel.socket: Failed with result 'service-start-limit-hit'.
[   26.142225] testsuite-17.sh[2074]: + udevadm control -l alert
[   26.149206] udevadm[2088]: Failed to send request to set log level: No such file or directory

Follow-up to: 6ef512c0bb