Fix FreeRTOS sockets for lwip 2.1.2
Problem detected in the SOPC_Socket_Connect function in p_sockets.c. With the new version of lwip (2.1.2) the access to errors has been changed to be closer to the posix operation. Previously, some errors were found with getsockopt() but now they are directly in errno. 3 functions fix : SOPC_Socket_Connect, SOPC_Socket_Write and SOPC_Socket_Read.