VETH Doc Update for pbourke

Single Adapter, Bonded Adapter, and VLANs - Oh My!
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Kolla can happily use a VETH adapter for network configuration.  This
along with OpenVSwitch or Linux native tools can allow for some fairly
creative networking setups.  For instance, in my test setup I use a
single adapter with VLANs for kolla.  First, I setup my OVS network:
root@c1n1:~# ovs-vsctl show
188f7b15-7e8d-4c40-a635-a247c2b43023
    Bridge "br1"
        Port mgmt
            tag: 50
            Interface mgmt
                type: internal
        Port "em1"
            tag: 51
            trunks: [50, 52, 60, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110]
            Interface "em1"
        Port "br1"
            Interface "br1"
                type: internal
    ovs_version: "2.5.0"

This is a pretty simple OVS setup, with a single NIC trunking vlans to 'br1'. Next I'm going to
add a 'gen' ('general') VETH pair to be used for the Kolla 'api network'. This traffic will be carried
over VLAN 101:
     ip link add genh type veth peer name gen
     ip addr add 192.168.101.11/24 dev gen
     ip link set gen up
     ip link set genh up
     ovs-vsctl add-port br1 genh
     ovs-vsctl set port genh tag=101

We created a pair of VETH devices (gen & genh), assigned an address/netmask to the 'interface' side, and added the 'host' (genh) side to the bridge.  Finally, we tag the traggic on the 'host side' (OVS Port).  This should give you:
root@c1n1:~# ovs-vsctl show
188f7b15-7e8d-4c40-a635-a247c2b43023
    Bridge "br1"
        Port mgmt
            tag: 50
            Interface mgmt
                type: internal
        Port "em1"
            tag: 51
            trunks: [50, 52, 60, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110]
            Interface "em1"
        Port "br1"
            Interface "br1"
                type: internal
        Port genh
            tag: 101
            Interface genh
    ovs_version: "2.5.0"

You can now use the 'interface' side of the VETH pair ('gen') as the 'api' or 'internal' network for Kolla by adding the
following to /etc/kolla/globals.yml:
  network_interface: "gen"
  kolla_internal_vip_address: "192.168.101.XX" # Chang to suite your setup

We can extend this to create an 'external' network as well:
     ip link add extrnlh type veth peer name extrnl
     ip addr add 192.168.60.11/24 dev extrnl
     ip link set extrnl up
     ip link set extrnlh up
     ovs-vsctl add-port br1 extrnlh
     ovs-vsctl set port extrnlh tag=60

Now you can use the 'extrnl' device and 192.168.60.0/24 as your 'external' network, with all traffic for it
being carried over VLAN 60. (NOTE: of course, you DO need your switches setup for the VLANs you use!)