OFPT_CHECKPOINT_ROLLBACK_REQUEST/REPLY start to implement.
 not implemented yet.
structure is complete.
	modified:   build-aux/check-structs
	modified:   include/openflow/openflow-1.1.h
	modified:   lib/learning-switch.c
	modified:   lib/ofp-msgs.h
	modified:   lib/ofp-print.c
	modified:   lib/ofp-util.c
	modified:   lib/ofp-util.h
	modified:   lib/rconn.c
	modified:   ofproto/ofp-ofctllib.c
	modified:   ofproto/ofp-ofctllib.h
	modified:   ofproto/ofproto.c
	modified:   utilities/ovs-checkpoint.c
	modified:   utilities/ovs-ofctl.c