BUG/MINOR: ssl: assert on SSL_set_shutdown with BoringSSL

BUG/MINOR: ssl: assert on SSL_set_shutdown with BoringSSL

With BoringSSL:
SSL_set_shutdown: Assertion `(SSL_get_shutdown(ssl) & mode) == SSL_get_shutdown(ssl)' failed.

"SSL_set_shutdown causes ssl to behave as if the shutdown bitmask (see SSL_get_shutdown)
were mode. This may be used to skip sending or receiving close_notify in SSL_shutdown by
causing the implementation to believe the events already happened.
It is an error to use SSL_set_shutdown to unset a bit that has already been set.
Doing so will trigger an assert in debug builds and otherwise be ignored.
Use SSL_CTX_set_quiet_shutdown instead."

Change logic to not notify on SSL_shutdown when connection is not clean.