Make packing PTR queries a bit more robust.•••There is no first party modules which could be compromised before
this check was added but its better to be safe wherever possible.
Make reading DNs more consistent across modules.•••- If the DN contains a new line character then replace it with a
space instead of killing the entire DN in the ssl_gnutls and
ssl_openssl modules.
- Apply the same logic to ssl_mbedtls which previously did not
handle spaces in DNs.