Thanks to Xogium for finding and debugging this!

Fixes: #2377

...with OpenSSL 1.1.0 or newer

Instead use TLS_server_method and
SSL_CTX_set_min_proto_version to limit
the used protocol versions.

According to the documentation the current option state is not cleared
but the options are added to the current options, so gettin the
current options seems redundant to the behavior of SSL_CTX_set_options:

> SSL_CTX_set_options() adds the options set via bitmask in options
> to ctx. Options already set before are not cleared!

Assigning the return value of SSLv23_server_method to a variable is
not necessary here and not doing it can get us rid of a lot of
condition code given that the type of the return value changed
at some point.

Explicitly initializing the library is not longer needed since
OpenSSL 1.1.0 and the SSL_library_init function is deprecated.

Citing the manual:

> As of version 1.1.0 OpenSSL will automatically allocate all resources
> that it needs so no explicit initialisation is required. Similarly it
> will also automatically deinitialise as required.

Fix #2318

Closes: #2348

See: #2358

See: #2370

Closes: #2370

Feature: Support HTTP keep-alive for SOURCE connections if they give us a content-length (useful for pokes)

For legacy-global-source this adds POST to the list.
For legacy-mount-source this adds POST and DELETE to the list.
The lists are now sync.

Closes: #2366
Found while working on & See also: icecast-libshout#2303

This updates to the Mozilla Foundation's "Intermediate" list
as of the time of this commit.
The list is appended with several negative rules that we included
before.

Closes: #2356

Closes: #2355