Setting MTU on VLAN does not set MTU on parent interface in 2.5.1
When altering the MTU on a VLAN, the physical interface needs to follow. Currently it does not, and you have to assign the parent and change it to match, or use some other manual means to set the MTU.
We need some extra logic to maintain that relationship on the backend, and possibly in the GUI as well, since changing one VLAN should change them all, and note that in the GUI.
Regression of [[https://redmine.pfsense.org/issues/2786]]