datapath-windows: Update vport add code.

datapath-windows: Update vport add code.

In this patch, we make the following updates to the vport add code:

1. Clarify the roles of the different hash tables, so it is easier to
   read/write code in the future.
2. Update OvsNewVportCmdHandler() to support adding bridge-internal
   ports.
3. Fixes in OvsNewVportCmdHandler() to support adding external port.
   Earlier, we'd hit ASSERTs.
4. I could not figure out way to add a port of type
   OVS_PORT_TYPE_INTERNAL with name "internal" to the confdb using
   ovs-vsctl.exe. And, this is needed in order to add the Hyper-V
   internal port from userspace. To workaround this problem, we treat a
   port of type OVS_PORT_TYPE_NETDEV with name "internal" as a request
   to add the Hyper-V internal port. This is a workaround. The end
   result is that there's a discrepancy between the port type in the
   datpaath v/s confdb, but this has not created any trouble in testing
   so far. If this ends up becoming an issue, we can mark the Hyper-V
   internal port to be of type OVS_PORT_TYPE_NETDEV. No harm.
5. Because of changes indicated in #1, we also update the vport dump
   code to look at the correct hash table for ports added from
   userspace.
6. Add a OvsGetTunnelVport() for convenience.
7. Update ASSERTs() while cleaning up the switch.
8. Nuke OvsGetExternalVport() and OvsGetExternalMtu().

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>