Add function that checks if the interface is part of a gateway group.
Add function that checks if the interface is part of a gateway group.

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