Send empty dict if no change for pg_id in flow stat
Send empty dict if no change for pg_id in flow stat

kisel/trex-core,dimagol/trex-core,dimagol/trex-core,dimagol/trex-core,dimagol/trex-core,dimagol/trex-core,kisel/trex-core,kisel/trex-core,dimagol/trex-core,kisel/trex-core,kisel/trex-core,kisel/trex-core