last, utmpdump, agetty, wall, write: avoid compatibility hacks

In include/bits/utmp.h the ut_user and ut_time macros are marked with
comment they are backwards compatibility hacks.  It is probably best to
avoid use of these macros where ever possible.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
utmpdump: make IPv6 addresses work

(unless bug[s]) This change is backwards compatibile.  Earlier binary to
text dumps can be converted back to binary, or otherway around.

The only thing that will not work are IPv6 addresses that possible
earlier conversion had broke.  Such conversions resulted with random IPv4
in place of IPv6 address in text format, and original information is gone
forever.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
tests: check last(1) and utmpdump(1) IPv6 functionality

Signed-off-by: Sami Kerola <kerolasa@iki.fi>