Simplify logic and fixes on interface_vlan_adapt_mtu()
Simplify logic and fixes on interface_vlan_adapt_mtu()

- Remove some redundant code and define $if_mtu respecting the order
	- Assinged interface
	- PPP
	- default
- When interface is a VLAN and parent is LAGG, it must be re-created

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