Sets the list of application-layer protocols to advertise that the
caller is willing to speak on this connection. The
Application-Layer Protocol Negotiation (ALPN) extension will be
used to negotiate a compatible protocol with the peer; use
g_dtls_connection_get_negotiated_protocol() to find the negotiated
protocol after the handshake. Specifying
NULL for the the value
protocols will disable ALPN negotiation.
See IANA TLS ALPN Protocol IDs for a list of registered protocol IDs.