[krbdev.mit.edu #3242] better debugging for krb5_os_localaddr

[Ken Raeburn via RT]

The t_localaddr program should be able to turn on debugging output with
a command-line flag.  That debugging output should trace the ioctl calls
we make (and the linux /proc ipv6 hackery), as well as dumping the
getifaddrs data that the DEBUG flag does currently.

Should this debug data be accessible from the normal library for
debugging purposes when people have binary distributions installed, as
in ticket 3237?  I dunno, haven't thought about it much.