bad: disable dtls test if openssl is not present

bad: disable dtls test if openssl is not present

On MacOS with homebrew, the openssl library is not
properly detected with pkg-config.
So disable the test compilation if openssl
is not properly detected along with libcrypto.

libcrypto is detected but it uses the system one
which leads to the error:

your binary is not an allowed client of /usr/lib/libcrypto.dylib for
architecture x86_64

See more details from Apple:

https://developer.apple.com/forums/thread/124782

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4483>