net: nsos_sockets: free allocated socket on close

Free the socket object allocated in `nsos_socket_create` when closing
the socket.

Signed-off-by: Jordan Yates <jordan@embeint.com>

drivers/net/nsos_sockets.c

@@ -256,6 +256,8 @@ static int nsos_close(void *obj)
 		errno = nsos_adapt_get_zephyr_errno();
 	}
 
+	k_free(sock);
+
 	return ret;
 }