Fix the get_network_id() function to always return a value
Fix the get_network_id() function to always return a value

Change-Id: Ib939db8dd2c7800470b879b1534e7a863b46a697

openstack/dragonflow,openstack/dragonflow,FrankDuan/df_code,FrankDuan/df_code,FrankDuan/df_code,openstack/dragonflow