VPNInstance IP Addr Family update is not working

VPNInstance IP Addr Family update is not working

Issue:
======
When router is getting associated with BGP-VPN(External BGP-VPN)
the corresponding external BGP-VPN
instance(odl-l3vpn:vpn-instance-op-data)
needs to be updated with IP address family based on the
attached subnets IP address family type either IPv4 or
IPv6 or both of them.

Currently updating the "vpn-instance-op-data" with
address family is not working as expected for some
times in odl cluster mode. (Sporadically this issue is happening)

If "vpn-instance-op-data" address family is not proper
then "ebgp:bgp" config data store also not proper as a
result address family (AFI/SAFI) is missing either IPv4
or IPv6 in ebgp data store in dual stack network use cases.

Solution:
============
As part of this issue fix reading "vpn-instance-op-data"
is avoided completely for updating VPN instance address family.
Since every time read and write into the DS is leading the
problem for dual stack network use cases.

So decided to re-implement the different approach of updating
the VPN Instance Op Data for address family. This will solve
race-condition between VPN Instance Op Data read and write.

Issue: NETVIRT-1410

Change-Id: I9dda8beeb74aaa273db800964b5e741478db36a3
Signed-off-by: Karthikeyan Krishnan <karthikeyangceb007@gmail.com>