inspector: restore 9229 as a default port

Some tools are now relying on 9229 to be node.js "inspector" port (I
see Chrome extensions, some online blog posts, etc.) Also, having same
default port values for old and new protocols may lead to some
confusion, e.g. when tools are trying to autodiscover debuggable Node
instances.

This is a partial revert of 9f1f7e2a. This commit preserves the fix for
issue #8201 bringing back the behavior that the old and new protocols
run on different ports.run on different ports.

PR-URL: https://github.com/nodejs/node/pull/8550


Reviewed-By: ofrobots - Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: cjihrig - Colin Ihrig <cjihrig@gmail.com>