errors,net: change internal/net.js to use internal/errors.js

Change internal/net.js so it makes use of the new internal/errors.js module.

See https://github.com/nodejs/node/issues/11273 for more info.

cc @jasnell

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

errors,net