SNAT traffic is getting dropped when gateway is removed from one router

SNAT traffic is getting dropped for second router when gateway is removed from first router.

Problem Description:
====================
Issue 1
+++++++

Consider the following topology.

1) 2 Internal Network + 2 Subnets
2) 2 Routers with each subnet associated to it.
3) One External network and both router associated to same External
Network.
4) One External BGPVN.

Now, when both Routers, if the same NAPT switch is elected, it will have a
common NAPT PFIB TABLE which forwards the outgoing packet. In such
scenario, when the gateway is removed for one of the routers,
this flow gets removed effecting the other routers traffic.

Issue 2
+++++++

Label of external-fixed-ip is freed from vpnservice pool when NAPT
switchover happens for SNAT.