The time takes in Logical Switch creation and tunnel I/F creation will increase dramatically when repeating l2gw node addition/deletion.

Issue：
We repeated l2gw node addition/deletion to Open vSwitch HWVTEP Emulator a few times.
The first 10 times, Logical Switch and tunnel I/F will be created in about 6 seconds after l2gw connection creation.
After 100 times, it will takes more than 300 seconds to finish Logical Switch and tunnel I/F creation.

Environment details:
OpenStack Version：stable/ocata
ODL Version：Carbon-FR + patch
patch: https://git.opendaylight.org/gerrit/#/c/56773/
https://git.opendaylight.org/gerrit/#/c/56710/
https://git.opendaylight.org/gerrit/#/c/58787/
https://git.opendaylight.org/gerrit/#/c/59598/
HWVTEP: Open vSwitch 2.6.1 HWVTEP Emulator
: HA Cluster

What we did (Steps):
1. L2GW Node Initialization:
a. delete L2GW GATEWAY/CONNECTION
b. stop OVS process and initialize
2. Network/subnet deletion:
neutron net-delete test-nw
3. Network/subnet creation:
neutron net-create test-nw
neutron subnet-create test-nw 192.168.0.0/24 --enable-dhcp
4. L2GW Node configuration
L2GW/LACP environment configuration
L2GW GATEWAY/CONNECTION creation
5. Wait until creation is completed
Wait until the VXLAN I/F is created in the OVS of the L2GW Node with a 3 seconds × 100 times loop
6. Communication confirmation (ping)
7. Go back to setp 1

Please check the log files attached.