Bug 8960: port information for 1 dpn is missing in subnet-op-data and

Bug 8960: port information for 1 dpn is missing in subnet-op-data and
port-op-data

Upon PL reboot , if southbound event (PortUP) event is received first and
northbound event(OnSubnetAddedToVpn) is received later ,DPN will not be
updated in PortOpData.

Fix :
(1) When northbound event is received , SubnetOpDataEntry is created first
by using clustered wide lock based on subnetId.
Then PortOpDataEntry and subnetToDpn is created.

(2)Incase southbound event is received first,PortOpData entry may not be
available.In such case subnetId is retrieved from Neutron cache and
PortOpData entry will be created by the SubnetInterfaceStateChangeListener
thread.

Change-Id: I92ed4aa801cfcbc2da37366149b7c5f2fba2ed4c
Signed-off-by: HANAMANTAGOUD V Kandagal <hanamantagoud.v.kandagal@ericsson.com>
Signed-off-by: ehvkand <hanamantagoud.v.kandagal@ericsson.com>