datapath-windows: loop iterator fixes in Vport.c

datapath-windows: loop iterator fixes in Vport.c

Validation:
- With these fixes, we no longer see the freeze during module
uninstallation or when we try to add a new port.
- We are able to add a port called "internal of type internal using:
ovs-dpctl.exe add-if ovs-system internal,type=internal

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