If we want to send a CONNECTION_CLOSE frame then one is enough unless we
are scheduled to send another one. Now that we can create more than one
datagram in one go this is now required.
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21798)