port-serial: add B230400 and B921600 missing baudrates

So MM can use them when opening a specific serial port.

Signed-off-by: Javier Viguera <javier.viguera@digi.com>

src/mm-port-serial.c

@@ -260,9 +260,15 @@ parse_baudrate (guint  baudrate_num,
     case 115200:
         speed = B115200;
         break;
+    case 230400:
+        speed = B230400;
+        break;
     case 460800:
         speed = B460800;
         break;
+    case 921600:
+        speed = B921600;
+        break;
     default:
         return FALSE;
     }