Stale Floating IP entry in dpn-op-elements

Stale Floating IP entry in dpn-op-elements

Problem Description:
It's been oberserved that the VM's neutron Port is
deleted first before floating-ip with which it associated. As a result,
when floating-ip-info delete event is triggered, the ifmgr RPC query to
get the DPNID first check for ietf-interface config (which is already
cleared) and return with empty DpnID. As a result, the flow for clear
the DNAT related flows and withdrawal of Floating IP route from
vpn-instance-op-data didn't succeeded.

Solution:
Change are to query the interface-state Oper DS to get the DPNID instead
of ifmmgr RPC call.

Change-Id: Ic12746e73e62d62b8310d391e51e42d376b465e4
Signed-off-by: Chetan Arakere Gowdru <chetan.arakere@altencalsoftlabs.com>