gst-bad 1.9.1 minor issue

[Alice Wonder]

The gstreamer-plugins-bad 1.9.1 if the TLS stack present is LibreSSL it 
will attempt to build the libgstdtls module and fail.

AFAIK LibreSSL doesn't actually implement DTLS.

The configure script should probably be fixed to check the OpenSSL 
implementation for the features needed for that module, and not just for 
whether the devel files are present.

No clue if this is an issue with earlier versions of GStreamer, 1.9.1 is 
first time building those plugins in a LibreSSL environment.

Build works as expected with openssl (where the module gets built) and 
as expected with no OpenSSL API dev package.

It's only a problem when the dev package is present but belongs to the 
LibreSSL fork of OpenSSL.