MINOR: ssl/sample: ssl_c_san returns a comma separated list of SAN

MINOR: ssl/sample: ssl_c_san returns a comma separated list of SAN

The ssl_c_san sample fetch returns a list of Subject Alt Name which was
presented by the client certificate.

The format is the same as the "openssl x509 -text" command, it's a
Description: Value list separated by commas.
The format is directly generated by the GENERAL_NAME_print() openssl
function.

https://github.com/openssl/openssl/blob/openssl-3.0/crypto/x509/v3_san.c#L207

Example:
    IP Address:127.0.0.1, IP Address:127.0.0.2, IP Address:127.0.0.3, URI:http://docs.haproxy.org/2.7/, DNS:ca.tests.haproxy.com