slabtop: for run_once switch (-o), output all slabinfo

slabtop: for run_once switch (-o), output all slabinfo

It doesn't make sense to restrict the number of output
lines to the total of terminal rows when using the run
once command line switch. And, in fact, that's how the
newlib version of slabtop works. Everything is output.

So, this commit places both versions on equal footing.

[ it was even worse if the switch was used in a pipe ]
[ since only 23 lines would have then been displayed ]

Signed-off-by: Jim Warner <james.warner@comcast.net>