STM32 DatagramSocket does not update automatically assigned private port number

[christiansiegel]

When binding an STM32 DatagramSocket to the port 0, FreeRTOS assigns an available port number from the private range (see FreeRTOS API Reference). However, the assigned port is not returned from SocketBind() in sdk/src/freertos/stm32f746g-discovery/socket.cc and DatagramSocket.port stays 0.