socket API is missing getlasterror()

[tabascoeye]

The socket API is missing a function to find out the last error that happened to a socket. if you don't have an "errno" mechanism in your system, this might be a good alternative to find out what specific error happened last on a socket.

[tabascoeye]

• add int lwip_getlasterror(int s); to src\include\lwip\socket.h
• add function in src\api\sockets.c

int lwip_getlasterror(int s)
{
  struct lwip_sock *sock = get_socket(s);
  if(sock){
    return(sock->err);
  } else {
    return(-1);
  }
}