BSN: Add network to ext_gw_info sent to backend

Include the full network info in the external gateway info
sent to the backend controller. This alleviates a very expensive
query across all tenants on the backend controller.

Closes-Bug: #1393991
Change-Id: If3601ccbce21e683924a7056cdfe4e3c2d4d4a93
Merge "BSN: Add network to ext_gw_info sent to backend"