selftests: netfilter: flowtable bridge and vlan support

This patch adds two new tests to cover bridge and vlan support:

- Add a bridge device to the Router1 (nsr1) container and attach the
  veth0 device to the bridge. Set the IP address to the bridge device
  to exercise the bridge forwarding path.

- Add vlan encapsulation between to the bridge device in the Router1 and
  one of the sender containers (ns1).

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>