For backward compatibility, the reader ignores VLAN_ID= if DEVICE= has a name with a suffix that looks like a vlan-id.
This was introduced by commit 10b32be3 ('ifcfg-rh: various VLAN cleanups').
In particular, when NetworkManager writes a profile to ifcfg format, then the profile must be encodable without modification. Since a NetworkManager profile has on consistency requirement that the vlan-id and the interface-name resemble each other, this requires a workaround.
Add a VLAN_ID_USE= flag. If that is true, then VLAN_ID= is preferred (if present).