DHCP fails as downstream packets are not trapped to ONOS

There is an intermittent issue that is seen with "master" where DHCP packets downstream are not trapped to ONOS.  In ONOS, subscribers stay at "DHCP REQUEST" state, while actual data plane still works.

Logs for the issue can be found here 

https://jenkins.opencord.org/view/VOLTHA-2.X-Tests/job/build_flex-ocp-cord_1T4GEM-bal31_voltha_master_test/150/ 

Check the logs for the failed test case.

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SubscriberId=ALPHe3d1ceb7-1,ConnectPoint=of:0000b86a974385f7/4112,State=DHCPREQUEST,MAC=B4:96:91:0C:4F:C9,CircuitId=ALPHe3d1ceb7-1,IP Allocated=0.0.0.0,Allocation Timestamp=2020-03-23T18:33:02.389520Z

SubscriberId=ALPHe3d1cea3-1,ConnectPoint=of:0000b86a974385f7/32,State=DHCPREQUEST,MAC=B4:96:91:0C:4F:E4,CircuitId=ALPHe3d1cea3-1,IP Allocated=0.0.0.0,Allocation Timestamp=2020-03-23T18:31:22.530800Z

SubscriberId=ALPHe3d1cfa7-1,ConnectPoint=of:0000b86a974385f7/16,State=DHCPREQUEST,MAC=B4:96:91:0C:4F:E5,CircuitId=ALPHe3d1cfa7-1,IP Allocated=0.0.0.0,Allocation Timestamp=2020-03-23T18:29:44.714460Z [?2004h