[BUG] Disabling BGP in a VRF crashes ebgp.multihop configuration templates

[ipspace]

Disabling BGP in a VRF results in a vdata.bgp data structure that has no neighbors (it only specifies the redistribution of connected routes into BGP). That mightily upsets ebgp.multihop configuration templates that expect to see bgp.neighbors whenever bgp is mentioned.

Lab topology

module: [ bgp, vrf ]
plugin: [ ebgp.multihop ]

vrfs:
  tenant:
    bgp: False
    links: [ dut-h1 ]

bgp.multihop.sessions:
- dut:
  pe2:

nodes:
  dut:
    bgp.as: 65000
  pe2:
    bgp.as: 65101
  h1:
    device: linux

links:
- dut-pe2

Proposed solution

As the final step in BGP module processing, make sure that the bgp data structure in every routing instance (if present) has bgp.neighbors list which can be empty.