zebra: Address sequencing issue while sending RMAC via FPM

zebra: Address sequencing issue while sending RMAC via FPM

Issue:
For consecutive messages such as
MAC1 -> VTEP1 add
MAC1 -> VTEP2 add
MAC1 -> VTEP1 add

Final state, i.e. (MAC1 -> VTEP1 add) should be sent via FPM.
But, with current code, FPM will send (MAC1 -> VTEP2 add)

RCA:
When FPM receives (MAC1, VTEP1), it stores it in the FPM processing queue and
hash table.

When FPM receives (MAC1, VTEP2), this entry is stored as another node as hash
table key is (mac, vtep and vni)

IF FPM again receives (MAC1, VTEP1), we fetch this node in the hash table
which is already enqueued.

When the FPM queue is processed, we will send FPM message for (MAC1, VTEP1)
first and then for (MAC1, VTEP2)

This sequencing issue happened because the key of the table is (MAC, VTEP, VNI)

Fix:
Change the key of the hash table to (MAC, VNI)
So, every time we receive a new update for (MAC1, VNI1), we will find a node in
the processing queue corresponding to MAC1 if present.
We will update this same node for every operation related to (MAC1, VNI1)

Thus, at the time when FPM processes this node, it will have latest MAC1 info.

Signed-off-by: Ameya Dharkar <adharkar@vmware.com>