datapaths: Fix port_mod/ofp rename
datapaths: Fix port_mod/ofp rename

_receive_port_mod() seems to have changed it parameter name from
'ofp' to the more specific 'port_mod', but it looks like this
patch wasn't completely applied.  Fixed.

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