Update STUN support to RFC 8489
STUN RFC 8489 obsoletes RFC 5389, adding new ciphersuites, DTLS support and various other changes
https://www.rfc-editor.org/rfc/rfc8489.html#section-19 shows the changes since RFC 5389
Due to an influx of spam, we have had to impose restrictions on new accounts. Please see this wiki page for instructions on how to get full permissions. Sorry for the inconvenience.
STUN RFC 8489 obsoletes RFC 5389, adding new ciphersuites, DTLS support and various other changes
https://www.rfc-editor.org/rfc/rfc8489.html#section-19 shows the changes since RFC 5389