MXS-2763: Log correct error for unsupported TLS versions

Previously when ssl_version was used with a value that is not supported on
the system, an unknown parameter error was returned. This could be
confusing and logging a proper error message should make it clear.

include/maxscale/ssl.h

@@ -31,13 +31,9 @@ struct dcb;
 
 typedef enum ssl_method_type
 {
-#ifndef OPENSSL_1_1
     SERVICE_TLS10,
-#endif
-#ifdef OPENSSL_1_0
     SERVICE_TLS11,
     SERVICE_TLS12,
-#endif
     SERVICE_SSL_MAX,
     SERVICE_TLS_MAX,
     SERVICE_SSL_TLS_MAX,