COLO-compare: Optimize compare_common and compare_tcp

Add offset args for colo_packet_compare_common, optimize
colo_packet_compare_icmp() and colo_packet_compare_udp()
just compare the IP payload. Before compare all tcp packet,
we compare tcp checksum firstly, this function can get
better performance.

Signed-off-by: Zhang Chen <zhangchen.fnst@cn.fujitsu.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
