lib, bgpd: changes for EAD-per-ES fragmentation

lib, bgpd: changes for EAD-per-ES fragmentation

The EAD-per-ES route carries ECs for all the ES-EVI RTs. As the number of VNIs
increase all RTs do not fit into a standard BGP UPDATE (4K) so the route needs
to be fragmented.

Each fragment is associated with a separate RD and frag-id -
1. Local ES-per-EAD -
ES route table - {ES-frag-ID, ESI, ET=0xffffffff, VTEP-IP}
global route table - {RD-=ES-frag-RD, ESI, ET=0xffffffff}
2. Remote ES-per-EAD -
VNI route table - {ESI, ET=0xffffffff, VTEP-IP}
global route table - {RD-=ES-frag-RD, ESI, ET=0xffffffff}

Note: The fragment ID is abandoned in the per-VNI routing table. At this
point that is acceptable as we dont expect more than one-ES-per-EAD fragment
to be imported into the per-VNI routing table. But that may need to be
re-worked at a later point.

CLI changes (sample with 4 VNIs per-fragment for experimental pruposes) -
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
root@torm-11:mgmt:~# vtysh -c "show bgp l2vpn evpn es 03:44:38:39:ff:ff:01:00:00:01"
ESI: 03:44:38:39:ff:ff:01:00:00:01
 Type: LR
 RD: 27.0.0.21:3
 Originator-IP: 27.0.0.21
 Local ES DF preference: 50000
 VNI Count: 10
 Remote VNI Count: 10
 VRF Count: 3
 MACIP EVI Path Count: 33
 MACIP Global Path Count: 198
 Inconsistent VNI VTEP Count: 0
 Inconsistencies: -
 Fragments: >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
  27.0.0.21:3 EVIs: 4
  27.0.0.21:13 EVIs: 4
  27.0.0.21:22 EVIs: 2
 VTEPs:
  27.0.0.22 flags: EA df_alg: preference df_pref: 32767
  27.0.0.23 flags: EA df_alg: preference df_pref: 32767

root@torm-11:mgmt:~# vtysh -c "show bgp l2vpn evpn es-evi vni 1002 detail"
VNI: 1002 ESI: 03:44:38:39:ff:ff:01:00:00:01
 Type: LR
 ES fragment RD: 27.0.0.21:13 >>>>>>>>>>>>>>>>>>>>>>>>>
 Inconsistencies: -
 VTEPs: 27.0.0.22(EV),27.0.0.23(EV)

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

PS: The number of EVIs per-fragment has been set to 128 and may need further
tuning.

Ticket: #2632967

Signed-off-by: Anuradha Karuppiah <anuradhak@nvidia.com>