flow_table: Fix FlowTable.flow_stats return value
flow_table: Fix FlowTable.flow_stats return value

Due to requiring accessing content by index and determination of length
of the return value, the return value is changed from a generator to
a list. This is ideal in face of any further complications.

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