qemu: Refresh rx-filters more often

qemu: Refresh rx-filters more often

There are couple of scenarios where we need to reflect MAC change
done in the guest:

  1) domain restore from a file (here, we don't store updated MAC
     in the save file and thus on restore create the macvtap with
     the original MAC),
  2) reconnecting to a running domain (here, the guest might have
     changed the MAC while we were not running),
  3) migration (here, guest might change the MAC address but we
     fail to respond to it,

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>