Vmware: Set correct nullable for lsn_id, nsx_port_id

Corrected the following models according to database
content:
- NOT NULL for LsnPort lsn_id;
- NOT NULL for NeutronNsxPortMapping nsx_port_id;

Partial-Bug: #1296282

Change-Id: Ia67fcc68eeceb27d9274adb652ab45b32152f01c
Merge "Vmware: Set correct nullable for lsn_id, nsx_port_id"