bgpd: VRF-Lite fix best path selection

bgpd: VRF-Lite fix best path selection

Description:
Incorrect behavior during best path selection for the imported routes.
Imported routes are always treated as eBGP routes.

Change is intended for fixing the issues related to
bgp best path selection for leaked routes:
- FRR does ecmp for the imported routes,
  even without any ecmp related config.
  If the same prefix is imported from two different VRFs,
  then we configure the route with ecmp even without
  any ecmp related config.
- Locally imported routes are preferred over imported
  eBGP routes.
  If there is a local route and eBGP learned route
  for the same prefix, if we import both the routes,
  imported local route is selected as best path.
- Same route is imported from multiple tenant VRFs,
  both imported routes point to the same VRF in nexthop.
- When the same route with same nexthop in two different VRFs
  is imported from those two VRFs, route is not installed as ecmp,
  even though we had ecmp config.

- During best path selection, while comparing the paths for imported routes,
  we should correctly refer to the original route i.e. the ultimate path.
- When the same route is imported from multiple VRF,
  use the correct VRF while installing in the FIB.
- When same route is imported from two different tenant VRFs,
  while comparing bgp path info as part of bgp best path selection,
  we should ideally also compare corresponding VRFs.

See-also: https://github.com/FRRouting/frr/files/7169555/FRR.and.Cisco.VRF-Lite.Behaviour.pdf

Co-authored-by: Santosh P K <sapk@vmware.com>
Co-authored-by: Kantesh Mundaragi <kmundaragi@vmware.com>
Signed-off-by: Iqra Siddiqui <imujeebsiddi@vmware.com>