Change the output of arp(8) to match what ndp(8) does and include the

Change the output of arp(8) to match what ndp(8) does and include the
expire timer.

This will makes it easier to add further information in a coherent way
between these tools for local and broadcast entries.

This new view displays either symbolic names (by default) or numerical
addresses (with "-n") for hosts but not both at the same time, just
like ndp(8), route(8) or netstat(1) do.

ok henning@