core: don't trigger OnFailure= deps when a unit is going to restart

core: don't trigger OnFailure= deps when a unit is going to restart

This adds a flags parameter to unit_notify() which can be used to pass
additional notification information to the function. We the make the old
reload_failure boolean parameter one of these flags, and then add a new
flag that let's unit_notify() if we are configured to restart the
service.

Note that this adjusts behaviour of systemd to match what the docs say.

Fixes: #8398