Recognize security_layer=negotiate in xrdp.ini, improve logging

security_layer=negotiate is documented, but the code is complaining
loudly about it. Fix it, make sure not to change the actual behavior
apart from the logging.

Improve the log message for unrecognized security_layer setting.

libxrdp/xrdp_rdp.c

@@ -182,10 +182,15 @@ xrdp_rdp_read_config(struct xrdp_client_info *client_info)
             {
                 client_info->security_layer = PROTOCOL_SSL | PROTOCOL_HYBRID;
             }
+            else if (g_strcasecmp(value, "negotiate") == 0)
+            {
+                client_info->security_layer = PROTOCOL_SSL | PROTOCOL_HYBRID | PROTOCOL_HYBRID_EX;
+            }
             else
             {
-                log_message(LOG_LEVEL_ALWAYS,"Warning: Your configured security layer is "
-                          "undefined, xrdp will negotiate client compatible");
+                log_message(LOG_LEVEL_ERROR, "security_layer=%s is not "
+                            "recognized, will use security_layer=negotiate",
+                            value);
                 client_info->security_layer = PROTOCOL_SSL | PROTOCOL_HYBRID | PROTOCOL_HYBRID_EX;
             }
         }