In case the if_vlan(4) interface has not been configured correctly, i.e. a bare interface without physical interface associated with it, retrieve the current settings and unconditionally overwrite params will lose vlandev settings. That will lead false report 'both vlan and vlandev must be specified'.
PR: 279181
Fixes: b82b8055ad44 ifconfig: fix vlan/vlanproto reconfiguration
MFC after: 3 days /* maybe should fast so catch up 14.1 ? */