addons: bridge: syntax check for illegal subintf as member of VLAN aware bridge

addons: bridge: syntax check for illegal subintf as member of VLAN aware bridge

Ticket: CM-12906
Reviewed By: Roopa, Nikhil G
Testing Done:

$ ifquery br0
auto br0
iface br0
      bridge-vlan-aware yes
      bridge-ports tap0 tap1.100
      bridge-vids 100 200
      bridge-pvid 1
      bridge-stp on

$ ifreload -a -s
error: br0: tap1.100: vlan sub-interface is not supported in a vlan-aware bridge
$

Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>