fib: improve ipv6 fib scaling

fib: improve ipv6 fib scaling

VPP IPv6 FIB relies on 2 bihash for all its VRFs: 1 for control plane
and one for data plane. Because of that, control plane VRF walks
time grows with the number of VRFs as it has to go through all the VRFs.
In order to improve control plane performance with large number of VRFs,
the control plane data structure is changed from a global bihash to a
per-VRF hashtable, similarly to IPv4. Contrary to IPv4, there is only 1
hashtable per VRF and not 1 hashtable per prefix-length per VRF, which
is a compromise between memory consumption and single VRF scaling.

Type: improvement

Change-Id: Ib738a44adb88e46c95c4c62c853ee1f1392c7187
Signed-off-by: Benoît Ganne <[email protected]>