COLO-compare: Fix incorrect `if` logic

COLO-compare: Fix incorrect `if` logic

'colo_mark_tcp_pkt' should return 'true' when packets are the same, and
'false' otherwise.  However, it returns 'true' when
'colo_compare_packet_payload' returns non-zero while
'colo_compare_packet_payload' is just a 'memcmp'.  The result is that
COLO-compare reports inconsistent TCP packets when they are actually
the same.

Fixes: f449c9e549c ("colo: compare the packet based on the tcp sequence number")
Cc: qemu-stable@nongnu.org
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Fan Yang <Fan_Yang@sjtu.edu.cn>
Signed-off-by: Jason Wang <jasowang@redhat.com>