Add support for new argument to vrouter-port-control

The vif.py invokes vrouter-port-control script with an additional argument. This new
argument is valid only for mainline, but since vif.py is present in a repo which is common
for R2.20, R2.21.x and R.22.x, vrouter-port-control script in branches R2.20, R2.21.x and
R.22.x should be updated to accept and ignore this argument.

Change-Id: I6c839e9a797b4992f7551216ca1d22a7a77cde9e
Closes-Bug: #1543936

src/vnsw/agent/port_ipc/vrouter-port-control

@@ -108,6 +108,7 @@ class VrouterPortControl(object):
         parser.add_argument("--tx_vlan_id", type = int, help = "Transmit VLAN ID")
         parser.add_argument("--rx_vlan_id", type = int, help = "Receive VLAN ID")
         parser.add_argument("--no_persist", type = bool, help = "Dont't store port information in files", default=False)
+        parser.add_argument("--vif_type", choices=['VhostUser', 'Vrouter'], help = "VIF type")
 
         self._args = parser.parse_args(remaining_argv)