net/colo-compare.c: Expose "compare_timeout" to users

net/colo-compare.c: Expose "compare_timeout" to users

The "compare_timeout" determines the maximum time to hold the primary net packet.
This patch expose the "compare_timeout", make user have ability to
adjest the value according to application scenarios.

QMP command demo:
    { "execute": "qom-get",
         "arguments": { "path": "/objects/comp0",
                        "property": "compare_timeout" } }

    { "execute": "qom-set",
         "arguments": { "path": "/objects/comp0",
                        "property": "compare_timeout",
                        "value": 5000} }

Signed-off-by: Zhang Chen <chen.zhang@intel.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>