doc,net: assign deprecation code

I missed this while landing 75a19fb3.

Ref: https://github.com/nodejs/node/pull/14449

I’d suggest to fast-track this as it’s a trivial fix (if CI is green).

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes (presumably, V8 is taking forever to compile and it’s not like there’s much I could have done wrong here 😄)
• commit message follows commit guidelines

Affected core subsystem(s)

net