This explicitly forbids an API pattern which formerly kind of worked, but was
extremely buggy (see preceding commits). Depending on how one interprets
close_notify and our API, one might wish to call SSL_shutdown only once
(morally shutdown(SHUT_WR)) and then SSL_read until EOF.
However, this exposes additional confusing states where we might try to send an
alert post-SHUT_WR, etc. Early commits made us more robust here (whether one is
allowed to touch the SSL* after an operattion failed because it read an alert
is... unclear), so we could support it if we wanted to, but this doesn't seem
worth the additional statespace. See if we can get away with not allowing it.
Change-Id: Ie7a7e5520b464360b1e6316c34ec9854b571782f
Reviewed-on: https://boringssl-review.googlesource.com/7433
Reviewed-by: David Benjamin <davidben@google.com>
c7eae5a326