Thread hangs in disconnect_socket

[devrandom]

Sometimes we get stuck in a busy loop here:

        while self.conn.lock().unwrap().block_disconnect_socket {
	        thread::yield_now();
        }

I think this is caused by one of the two places that has the following structure:

	if let Err(e) = peer_manager.write_buffer_space_avail(&mut our_descriptor) {
		shutdown_socket!(e, Disconnect::CloseConnection);
	}
	us.lock().unwrap().block_disconnect_socket = false;

since shutdown_socket! jumps out of the surrounding loop.

The last log entry was:

2021-06-13 17:01:03 TRACE [lightning::ln::peer_handler:1370] Disconnecting peer with id 03cef01527340b029e2b4a6293b98190e4e51b7c07b5e49b6412a7d4edd3b0d03d due to ping timeout

[devrandom]

I can sometimes replicate this by pausing a node in the debugger and restarting it after the ping timeout.

[TheBlueMatt]

Fixed by #957. If there's more left let's open a new issue.