net: bridge: fix returning of vlan range op errors

When vlan tunnels were introduced, vlan range errors got silently
dropped and instead 0 was returned always. Restore the previous
behaviour and return errors to user-space.

Fixes: efa5356b ("bridge: per vlan dst_metadata netlink support")
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>