bridge: T5670: add missing constraint on "member interface" node

One could specify a bridge member of VXLAN1 interface, but it is not possible
to create a VXLAN interface with the name of VXLAN1 - prohibited by VXLAN
interface name validator.

Add missing interface-name validator code

(cherry picked from commit 45dc149e4e3c0c294deac6fd541bb027d2280ea1)