[sslh] Add ALPN protocol based probe

[moparisthebest]

On 12/16/2015 02:43 PM, moparisthebest wrote:
> This time I'm back with an ALPN probe patch, posted on github here:
> https://github.com/yrutschle/sslh/pull/74

I was thinking a little more about this patch, and realized since the
previous SNI patch hasn't made an official release yet, it might
possibly make it cleaner to just have the name of all of these be 'tls'
instead of 'sni' or 'alpn', since both are TLS Extensions.  The code
changes would be minimal, as it already treats sni/alpn as identical,
instead looking at whether alpn_protocols and/or sni_hostnames is set
and basing the probe on that anyhow...

Anyway, that's a question for the maintainer, if you like that idea I'll
modify this patch to do so.