openflow.nicira: Only enable extensions for OVS
openflow.nicira: Only enable extensions for OVS

Previously, as long as openflow.nicira was loaded, all switches were
treated as if they supported those extensions.  We now check to see if
the switch actually appears to be OVS.

noxrepo/pox,noxrepo/pox,noxrepo/pox,pthien92/sdn,pthien92/sdn,pthien92/sdn,MurphyMc/pox,MurphyMc/pox,MurphyMc/pox,noxrepo/pox,MurphyMc/pox,pthien92/sdn,pthien92/sdn,MurphyMc/pox