net/colo: Match is-enabled probe to tracepoint

Build of QEMU with dtrace fails on macOS:

  LINK    x86_64-softmmu/qemu-system-x86_64
error: probe colo_compare_miscompare doesn't exist
error: Could not register probes
ld: error creating dtrace DOF section for architecture x86_64

The reason of the error is explained by Adam Leventhal [1]:

  Note that is-enabled probes don't have the stability magic so I'm not
  sure how things would work if only is-enabled probes were used.

net/colo code uses is-enabled probes to determine if other probes should
be used but colo_compare_miscompare itself is not used explicitly.
Linker doesn't include the symbol and build fails.

The issue can be resolved if is-enabled probe matches the actual trace
point that is used inside the test. Packet dump toggle is replaced with
a compile-time conditional definition.

1. http://markmail.org/message/6grq2ygr5nwdwsnb



Fixes: f4b61836 ("colo-compare: add TCP, UDP, ICMP packet comparison")
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: Cameron Esfahani <dirty@apple.com>
Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Reviewed-by: Zhang Chen <chen.zhang@intel.com>
Message-id: 20200717093517.73397-5-r.bolshakov@yadro.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>