datapath-windows: OvsFindVportByPortIdAndNicIndex() and external port.

We use OvsFindVportByPortIdAndNicIndex() to lookup the vport for a
packte received from the Hyper-V switch. If a packet was indeed received
from the virtual external NIC, we should flag it.

Validation:
1. Install and Uninstall the OVS EXT Driver (without enabling the OVS
   extension on the Hyper-V switch).
2. Install and Uninstall the OVS EXT Driver (with enabling the OVS
   extension on the Hyper-V switch). Hyper-V switch had a few ports.
3. Install and Uninstall the OVS EXT Driver (with enabling the OVS
   extension on the Hyper-V switch). Added a few ports before
   uninstalling.
4. Install the OVS EXT driver, and test the following functionality:
   a) ping between 2 VMs on the same host
   b) ping between 2 VMs on 2 Hyper-Vs - one physical and another
      virtual backed by VLAN (patch port between br-pif and br-int).
   c) ping between 2 VMs on 2 Hyper-Vs - one physical and another
      virtual backed by VXLAN.
   d) Successful uninstallation after these tests.

Signed-off-by: Nithin Raju <nithin@vmware.com>
Acked-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Tested-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Acked-by: Ankur Sharma <ankursharma@vmware.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>