net: wait for shutdown to complete before closing

When not allowing half open, handle.close would be
invoked before shutdown has been called and
completed causing a potential data race.

Fixes: https://github.com/nodejs/node/issues/32486#issuecomment-604072559

PR-URL: https://github.com/nodejs/node/pull/32491


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>