flow_table: add underscore to private member
flow_table: add underscore to private member

The way the json encoder works right now for NOM objects is that it
only serializes members that do not begin with an underscore

PrincetonUniversity/pox,chenyuntc/pox,kulawczukmarcin/mypox,adusia/pox,chenyuntc/pox,diogommartins/pox,denovogroup/pox,jacobq/csci5221-viro-project,diogommartins/pox,PrincetonUniversity/pox,adusia/pox,chenyuntc/pox,kavitshah8/SDNDeveloper,andiwundsam/_of_normalize,kpengboy/pox-exercise,noxrepo/pox,andiwundsam/_of_normalize,VamsikrishnaNallabothu/pox,chenyuntc/pox,noxrepo/pox,xAKLx/pox,carlye566/IoT-POX,MurphyMc/pox,diogommartins/pox,carlye566/IoT-POX,MurphyMc/pox,pthien92/sdn,MurphyMc/pox,waltznetworks/pox,noxrepo/pox,MurphyMc/pox,kpengboy/pox-exercise,carlye566/IoT-POX,pthien92/sdn,waltznetworks/pox,carlye566/IoT-POX,MurphyMc/pox,VamsikrishnaNallabothu/pox,pthien92/sdn,xAKLx/pox,VamsikrishnaNallabothu/pox,PrincetonUniversity/pox,diogommartins/pox,andiwundsam/_of_normalize,kpengboy/pox-exercise,denovogroup/pox,andiwundsam/_of_normalize,kulawczukmarcin/mypox,kavitshah8/SDNDeveloper,kulawczukmarcin/mypox,jacobq/csci5221-viro-project,kulawczukmarcin/mypox,VamsikrishnaNallabothu/pox,diogommartins/pox,kpengboy/pox-exercise,chenyuntc/pox,adusia/pox,noxrepo/pox,adusia/pox,xAKLx/pox,jacobq/csci5221-viro-project,waltznetworks/pox,adusia/pox,VamsikrishnaNallabothu/pox,waltznetworks/pox,PrincetonUniversity/pox,denovogroup/pox,kavitshah8/SDNDeveloper,denovogroup/pox,waltznetworks/pox,denovogroup/pox,xAKLx/pox,jacobq/csci5221-viro-project,PrincetonUniversity/pox,kpengboy/pox-exercise,carlye566/IoT-POX,kulawczukmarcin/mypox,pthien92/sdn,jacobq/csci5221-viro-project,xAKLx/pox,pthien92/sdn,kavitshah8/SDNDeveloper