bsd_close_socket preserves the error code

[aditmak]

I am using the uWebsocket application. When I call the application's listen function to open the port and begin listening it failed.
Because the application failed to listen, it closes the socket and exits gracefully. So, if there is an error while opening the port, the errno variable is updated with the error code then the close socket function is called and it updates the errno, causing the error information from the listening socket failure to be lost.
By preserving the errno after the close socket function, the real error can be determined.