zebra: fix a problem with local MAC pointing to a remote ES

zebra: fix a problem with local MAC pointing to a remote ES

If a remote MAC update is rxed from BGP with a lower sequence number than
the local one zebra ignores the MAC update. This typically happens if
there is a race condition (where updates are in flight from zebra to BGP).

There was a bug in zebra because of which the dest ES was being updated
before this check. This left the local MAC pointing to a remote ES.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Relevant Dumps:
===============
root@leaf21:mgmt:~# net show evpn mac vni 101101 mac 00:93:00:00:00:01
MAC: 00:93:00:00:00:01
 ESI: 03:00:00:00:77:01:03:00:00:0d
 Intf: - VLAN: 101
 Sync-info: neigh#: 1 peer-proxy
 Local Seq: 3 Remote Seq: 0
 Neighbors:
    21.1.13.1 Active
root@leaf21:mgmt:~# net sho evpn es
Type: L local, R remote, N non-DF
ESI                            Type ES-IF                 VTEPs
03:00:00:00:77:01:02:00:00:0c  R    -                     6.0.0.10,6.0.0.11
03:00:00:00:77:01:03:00:00:0d  R    -                     6.0.0.10,6.0.0.11,6.0.0.12
03:00:00:00:77:01:04:00:00:0e  R    -                     6.0.0.10,6.0.0.11,6.0.0.12,6.0.0.13
03:00:00:00:77:02:02:00:00:16  LR   bondP2-H2             6.0.0.15
03:00:00:00:77:02:03:00:00:17  LR   bondP2-H3             6.0.0.15,6.0.0.16
03:00:00:00:77:02:04:00:00:18  LR   bondP2-H4             6.0.0.15,6.0.0.16,6.0.0.17
root@leaf21:mgmt:~#

Relevant logs:
===============
2020/07/29 15:41:27.110846 ZEBRA: Recv MACIP ADD VNI 101101 MAC 00:93:00:00:00:01 IP 21.1.13.1 flags 0x0 seq 2 VTEP 0.0.0.0 ESI 03:00:00:00:77:01:03:00:00:0d from bgp
2020/07/29 15:41:27.110867 ZEBRA: Ignore remote MACIP ADD VNI 101101 MAC 00:93:00:00:00:01 IP 21.1.13.1 as existing MAC has higher seq 3 flags 0x401
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Ticket: CM-30273

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