datapaths: Clean/extend connection error handling
datapaths: Clean/extend connection error handling

OFConnection's error handling didn't send error messages for bad
message type or bad message length.  Added.

Also refactored the error handling to be cleaner / more regular.

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