there are spec non-conformance in 4.4BSD tftpd/tftp.
	if we strictly follow RFC1350, we should allow IP address pairs to be
	switched - we should validate connection based on udp src/dst port
	number only.

	4.4BSD tftpd calls connect(2), which forbids us to change IP address
	pairs.  NetBSD tftpd is worse because it calls bind(2) with
	non-wildcard address as well.  4.4BSD tftp trusts server too much
	(always copies port number got from recvfrom).

	question - are there any other implementation that chokes, if we
	correct it?

	(the fix suggestion is from jinmei@kame.net)

itojun