Support for VRRP with rfc3768 using i40e NICs

In case if VRRP used on NICs based on i40e driver, like Intel X710/X722 with rfc3768-compatibility necessary to disable pruning sources. The best way is to use /config/scripts/vyos-postconfig-bootup.script and add the following command:

ethtool --set-priv-flags ethX disable-source-pruning on