get_parent_interface() - add support for vlans configured as a vlan but not an interface
get_parent_interface() - add support for vlans configured as a vlan but not an interface

One scenario when this happens is a vlan used solely as a PPPoE port.

pfsense/pfsense,jxmx/pfsense,ch1c4um/pfsense,BlackstarGroup/pfsense,phil-davis/pfsense,ptorsten/pfsense,BlackstarGroup/pfsense,ptorsten/pfsense,NOYB/pfsense,brunostein/pfsense,NOYB/pfsense,brunostein/pfsense,NewEraCracker/pfsense,NewEraCracker/pfsense,pfsense/pfsense,phil-davis/pfsense,BlackstarGroup/pfsense,dennypage/pfsense,jxmx/pfsense,NewEraCracker/pfsense,dennypage/pfsense,NewEraCracker/pfsense,jxmx/pfsense,NOYB/pfsense,ch1c4um/pfsense,ptorsten/pfsense,dennypage/pfsense,ch1c4um/pfsense,phil-davis/pfsense,brunostein/pfsense,pfsense/pfsense,pfsense/pfsense,dennypage/pfsense,ch1c4um/pfsense,phil-davis/pfsense,BlackstarGroup/pfsense