Now that we have @flags we can support changing perf events just
in active or inactive configuration regardless of the other.
Previously, calling virDomainSetPerfEvents set events in both
active and inactive configuration at once. Even though we allow
users to set perf events that are to be enabled once domain is
started up. The virDomainGetPerfEvents API was flawed too. It
returned just runtime info.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>