Revision 330696

Add some functional tests for tftpd(8)

tftpd(8) is difficult to test in isolation due to its relationship with
inetd.  Create a test program that mimics the behavior of tftp(1) and
inetd(8) and verifies tftpd's response in several different scenarios.

These test cases cover all of the basic TFTP protocol, but not the optional
parts.

PR:		157700
PR:		225996
PR:		226004
PR:		226005
MFC after:	3 weeks
Differential Revision:	https://reviews.freebsd.org/D14310