datapath-windows: Update OvsGetExtInfoIoctl() to the new vport add workflow

I applied the patches for the new vport add workflow that is out for
review, and found that some of the existing code in OvsGetExtInfoIoctl()
needs to be updated. In this patch, we add a CPP called
USE_NEW_VPORT_ADD_WORKFLOW and add the fixes under
USE_NEW_VPORT_ADD_WORKFLOW == 1. The current value is set to 0, since
the vport add code is not checked in yet.

Sending out this patch to unblock the vport add code when it gets checked
in. There are other fixes also required, but they are being addressed as
part of the review comments for vport-add.

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