streams: support unlimited synchronous cork/uncork cycles

net streams can request multiple chunks to be written in a synchronous
fashion. If this is combined with cork/uncork, en error is currently
thrown because of a regression introduced in:
https://github.com/nodejs/node/commit/89aeab901ac9e34c79be3854f1aa41f2a4fb6888
(https://github.com/nodejs/node/pull/4354).

Fixes: https://github.com/nodejs/node/issues/6154
PR-URL: https://github.com/nodejs/node/pull/6164


Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Mathias Buus <mathiasbuus@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>