inherit the behaviour of B<fd>. If B<fd> is nonblocking, the B<ssl> will
also have nonblocking behaviour.
+When used on a QUIC SSL object, a B<datagram BIO> is automatically created
+instead of a B<socket BIO>.
+
If there was already a BIO connected to B<ssl>, BIO_free() will be called
(for both the reading and writing side, if different).