libopenflow: More work fixing up stats
libopenflow: More work fixing up stats

This primarily makes the packing and unpacking of stats
messages cleaner.

Also renames ofp_action to ofp_action_base, adds some comments,
etc.

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