Adding Network MTU parameter to VLANs

Change-Id: Id0aefc4a8ee8e07ec74ef4a519d646e9fc0120ec
diff --git a/_modules/maasng.py b/_modules/maasng.py
index f14b18e..a96a4e4 100644
--- a/_modules/maasng.py
+++ b/_modules/maasng.py
@@ -1082,7 +1082,7 @@
     return ret
 
 
-def create_vlan_in_fabric(name, fabric, vlan, description, primary_rack,
+def create_vlan_in_fabric(name, fabric, vlan, description, primary_rack, mtu=1500,
                           dhcp_on=False, update=False, vlan_id=""):
     """
     Update vlan
@@ -1095,6 +1095,7 @@
     data = {
         "name": name,
         "dhcp_on": str(dhcp_on),
+        "mtu": mtu,
         "description": description,
         "primary_rack": list_racks()[primary_rack]['system_id'],
     }