Suggested-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

iPXE is fundamentally asynchronous in operation: some operations
continue in the background even after the foreground has continued to
a new task.  For example, the closing FIN/ACK exchanges of a TCP
connection will take place in the background after an HTTP download
has completed.

Signed-off-by: Michael Brown <mcb30@ipxe.org>