Extend the testing of resetting/clearing an SSL connection

Extend the testing of resetting/clearing an SSL connection

SSL_clear() explicitly clears an SSL object to enable it to be reused.
You can have a similar effect by calling SSL_set_accept_state() or
SSL_set_connect_state(). We extend the testing of SSL_clear() to use these
other methods. We also ensure we test the case where we have unread
bufferred data that needs to be cleared.

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23256)