spanning_tree: Minor improvements
spanning_tree: Minor improvements

* Add comments
* More conservative behavior when switches reconnect
* A bit of modernization

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