### Description

After adding TLS support to the CDP module, it's no longer possible to load on systems running a version of openssl older than 1.1.1.

#### Reproduction

Run on system with openssl older than 1.1.1.

#### Log Messages

<!-- Check the syslog file and if there are relevant log messages printed by Kamailio, add them next, or attach to issue, or provide a link to download them (e.g., to a pastebin site). -->

``` ERROR: <core> [core/sr_module.c:599]: ksr_load_module(): could not open module </usr/local/kamailio-devel/lib64/kamailio/modules/cdp.so>: /usr/local/kamailio-devel/lib64/kamailio/modules/cdp.so: undefined symbol: SSL_CTX_set_max_proto_version ```

### Possible Solutions

I've made a local change based on the approach used in the tls module for different versions of openssl. Do you want me to open a PR for this, or do you want this module clean?

Currently I do not have any possibility to test it's actually working, but at least it compiles/loads and makes to module possible to use without encryption.

Another solution might be to just include TLS support if the openssl version on the system is 1.1.1 or newer. Else, just do not support it.

### Additional Information

* **Kamailio Version** - output of `kamailio -v`

``` master ```

* **Operating System**:

<!-- Details about the operating system, the type: Linux (e.g.,: Debian 8.4, Ubuntu 16.04, CentOS 7.1, ...), MacOS, xBSD, Solaris, ...; Kernel details (output of `lsb_release -a` and `uname -a`) -->

``` CentOS 7.9 ```