fix the check for content-type

kamailio/message-role.cfg

@@ -12,8 +12,8 @@ route[HANDLE_MESSAGE]
        sl_send_reply("403", "Forbidden");
        exit;
     } else {
-       if($hdr(Content-Type) == "text/plain" ||
-          $hdr(Content-Type) == "text/html") {
+       if($hdr(Content-Type) =~ "text/plain" ||
+          $hdr(Content-Type) =~ "text/html") {
            route(MESSAGE_INBOUND);
        } else {
            xlog("L_WARN", "$ci|end|dropping MESSAGE $hdr(Content-Type)\n");