rwhod(8): Prevent clobbering the neighboring field by a wrong cast.
The time stamps in the rwhod(8) network datagram and, based on that,
/var/rwho/whod.* spool files are typed as 32bit int and cannot accept
a 64bit time_t.
The old code clobbered the first bytes of the adjacent "hostname"
field, yielding empty hostnames in local rwho(1) and ruptime(1) output.
(Outgoing datagrams to other hosts were not affected.)
Re-code to let the compiler do the proper coercion (well, until 2038).
Submitted-by: Martin Neitzel
Dragonfly-bug: <https://bugs.dragonflybsd.org/issues/2339>