netifd: resolve regression on ex400 due to 8021ad name change
Support for 8021ad interface with name ethx.y.z is restricted to broadcom platform having vlanconf for now. This resolves the regression on ex400 when both switch and device section are present and device section is used only to configure mac address on the pre-existing interface on the switch.
Test:
- 8021ad interface with name ethx.y.z is supported on panther.
- regression tests for all deployments on panther pass.
- ssh and ping to ex400 is possible.
- wan interface on ex400 can get the IP address from upstream dhcp server.