colo-compare: introduce packet comparison thread

If primary packet is same with secondary packet,
we will send primary packet and drop secondary
packet, otherwise notify COLO frame to do checkpoint.
If primary packet comes but secondary packet does not,
after REGULAR_PACKET_CHECK_MS milliseconds we set
the primary packet as old_packet,then do a checkpoint.

Signed-off-by: Zhang Chen <zhangchen.fnst@cn.fujitsu.com>
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
