update: add on-port check when kernel-tracing

[RafaelGSS]

Reference: https://github.com/clinicjs/node-clinic-flame/issues/171.

I haven't found an valid approach to pipe between a non-nodejs process. To summarize the problem:

When no kernel-tracing:

• Root process spawn a new Node.js process
• The communication happens using a new fd (created using the stdio option).

When kernel-tracing:

• Root process spawn a non-nodejs process that spawn a nodejs process (nodejs -> linux_perf -> nodejs)
• So, the communication between the root process and nodejs doesn't work.

The best option so far is improving the UX by throwing an error when both options are used together, instead quitting silently

[mcollina]

lgtm