Add more priority than the gnutls backend

If someone is installing this backend is because of the need for
this backend instead of gnutls. i.e to keep consistency between
windows and linux or to provide support for a tls backend on an
old system, i.e the still supported by red hat rhel 6

tls/openssl/gtlsbackend-openssl.c

@@ -260,5 +260,5 @@ g_tls_backend_openssl_register (GIOModule *module)
   g_io_extension_point_implement (G_TLS_BACKEND_EXTENSION_POINT_NAME,
                                   g_tls_backend_openssl_get_type(),
                                   "openssl",
-                                  0);
+                                  100);
 }