Fix error in BIO_get_ktls_send() and BIO_get_ktls_recv()

If we were using a different type of BIO than a socket BIO then
BIO_get_ktls_send() and BIO_get_ktls_recv() could return the wrong
result.

The above occurred even if KTLS was disabled at compile time - so we should
additionally ensure that those macros do nothing if KTLS is disabled.

Finally we make the logic in ssl3_get_record() a little more robust when
KTLS has been disabled.

[extended tests]

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8793)