Configure dhcp relay in Maas fabrics

PROD-31910

Change-Id: I80d5a15fc38be0793c680da8c6bfd24b2e9f407e
diff --git a/_modules/maasng.py b/_modules/maasng.py
index c2676c1..4002e05 100644
--- a/_modules/maasng.py
+++ b/_modules/maasng.py
@@ -1416,7 +1416,7 @@
 
 
 def create_vlan_in_fabric(name, fabric, vlan, description, primary_rack, mtu=1500,
-                          dhcp_on=False, update=False, vlan_id=""):
+                          dhcp_on=False, update=False, vlan_id="", relay_vlan=None):
     """
     Update vlan
     CLI Example:
@@ -1433,6 +1433,8 @@
     }
     if mtu:
         data['mtu'] = str(mtu)
+    if relay_vlan:
+        data['relay_vlan'] = str(relay_vlan)
     vlan = str(vlan)
     maas = _create_maas_client()
     fabric_id = get_fabricid(fabric)