Supports MTU option in OpenstackSwitching dhcp handler.

Change-Id: Ic3b712814d20d17b32dc66963a0845291828c97b
diff --git a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingDhcpHandler.java b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingDhcpHandler.java
index 0b751e6..3a11e5a 100644
--- a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingDhcpHandler.java
+++ b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingDhcpHandler.java
@@ -62,6 +62,7 @@
 import org.onosproject.openstacknode.api.OpenstackNodeService;
 import org.openstack4j.model.network.HostRoute;
 import org.openstack4j.model.network.IP;
+import org.openstack4j.model.network.Network;
 import org.openstack4j.model.network.Port;
 import org.openstack4j.model.network.Subnet;
 import org.osgi.service.component.ComponentContext;
@@ -87,6 +88,7 @@
 import static org.onosproject.openstacknetworking.api.Constants.DHCP_ARP_TABLE;
 import static org.onosproject.openstacknetworking.api.Constants.PRIORITY_DHCP_RULE;
 import static org.onosproject.openstacknode.api.OpenstackNode.NodeType.COMPUTE;
+import static com.google.common.base.Preconditions.checkNotNull;
 import static org.slf4j.LoggerFactory.getLogger;
 
 /**
@@ -425,7 +427,11 @@
             option = new DhcpOption();
             option.setCode(DHCP_OPTION_MTU);
             option.setLength((byte) 2);
-            option.setData(ByteBuffer.allocate(2).putShort((short) dhcpDataMtu).array());
+            Network osNetwork = osNetworkService.network(osSubnet.getNetworkId());
+            checkNotNull(osNetwork);
+            checkNotNull(osNetwork.getMTU());
+
+            option.setData(ByteBuffer.allocate(2).putShort(osNetwork.getMTU().shortValue()).array());
             options.add(option);
 
             // classless static route