flow_table: Minor cleanup
flow_table: Minor cleanup

This cleans up/improves some comments, removes an unused method, and makes
other minor stylistic improvements.  Perhaps most notably, it adds an
"effective_priority" attribute to flow entries which is "infinitely" high
when the entry is an exact-match entry.

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