units: disable start rate limit for systemd-vconsole-setup.service

units: disable start rate limit for systemd-vconsole-setup.service

The unit will be started or restarted a few times during boot, but but it has
StartLimitBurst = DefaultStartLimitBurst = 5, which means that the fifth
restart will already fail. On my laptop, I have exactly 4 restarts, so I don't
hit the limit, but on a slightly different system we will easily hit the limit.
In https://bugzilla.redhat.com/show_bug.cgi?id=2251394, there are five reloads
and we hit the limit.

Since 6ef512c0bb7aeb2000588d7d05e23b4681da8657 we propagate the start counter
over switch-root and daemon reloads, so it's easier to hit the limit during
boot.

In principle there might be systems with lots of vtcon devices, so let's just
allow the unit to be restarted without a limit.

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=2251394.