Do not use VLANMTU flag to decide if interface supports to run VLAN
Today there is a function called is_jumbo_capable() that detects if VLANMTU flag is supported by interface and this function is used to build the list of available parent interfaces to configure VLANs.
VLANMTU means interface can do 1500 MTU even using VLAN. Not having it is not a blocker to setup VLAN on the interface. Fix the code removing this check, but make sure only physical interfaces are being listed.