BUG/MINOR: quic: Possible crash with "tls-ticket-keys" on QUIC bind lines

BUG/MINOR: quic: Possible crash with "tls-ticket-keys" on QUIC bind lines

ssl_tlsext_ticket_key_cb() is called when "tls-ticket-keys" option is used on a
"bind" line. It needs to have an access to the TLS ticket keys which have been
stored into the listener bind_conf struct. The fix consists in nitializing the
<ref> variable (references to TLS secret keys) the correct way when this callback
is called for a QUIC connection. The bind_conf struct is store into the quic_conn
object (QUIC connection).

This issue may be in relation with GH #1851. Thank you for @tasavis for the report.

Must be backported to 2.6.