Updates according to comments for Operational and Functional tests for CORD certification

Change-Id: I3e972fe7f6f85f1b95dd729d6d41f6319a52c8b4
diff --git a/Fabric/Utilities/src/python/oftest/dataplane.py b/Fabric/Utilities/src/python/oftest/dataplane.py
index df79d47..839fe9e 100644
--- a/Fabric/Utilities/src/python/oftest/dataplane.py
+++ b/Fabric/Utilities/src/python/oftest/dataplane.py
@@ -132,6 +132,13 @@
         #os.system("ifconfig up %s" % self.interface_name)
         os.system("ifconfig %s up" % self.interface_name)
 
+    def mtu(self, mtu):
+        """
+        Change MTU value of port.
+        """
+        # os.system("ifconfig up %s" % self.interface_name)
+        os.system("ifconfig %s mtu %d" % (self.interface_name, mtu))
+
 
 class DataPlanePortPcap:
     """
@@ -392,3 +399,7 @@
         if self.pcap_writer:
             self.pcap_writer.close()
             self.pcap_writer = None
+
+    def port_mtu(self, port_number, mtu):
+        """Change MTU on controller's port"""
+        self.ports[port_number].mtu(mtu)