Fix for flow stats - making functions virtual
Fix for flow stats - making functions virtual

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