l2_learning: Some cleanup / updating
l2_learning: Some cleanup / updating

* Switch from using some deprecated stuff
* Use new packet_in resend capability
* Improve some comments / docstrings
* Fix some wrapping

I didn't test this at all, so...

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