enable l2arc stats

missing newline

include compressed l2size

Remove lines which don't function under zfs on linux.
Fix bug in arc_summary.py, -p option now works.

The -p option is designed to specify which page of output to display. It
wasn't working because the function that gathers statistics, get_Kstat
was only being called in the 'call_all' function which was never called
if the -p option was in place. Owing to this, an exception would be
raised in the option handling code in the main function, which would
then call 'call_all', causing all pages of output to display,
effectively negating the point of the -p option.

This fix ensures that get_Kstat is called in the main function, thus
enabling a single page of output to be displayed without running into an
exception.
Refactor arc_summary to simplify -p processing

The -p option is used to specify a specific page of output to be
displayed. If omitted, all output pages would be displayed.

arc_summary, as it stood, had really kludgy processing code for
processing the -p option. It relied on a try-except block which was
treated as an if statement and in normal operation would fail any time a
user didn't specify the -p option on the command line. When the
exception was thrown, the script would then display all output pages.
This happened whether the -p option was omitted or malformed. Thus, in
the principle use case, an exception would be raised in order to run the
script as desired. The same except code would be called regardless of
the exception, however, and malformed -p arguments would also cause the
script to execute.

Additionally, this required the function which handles the case where
all output pages were to be displayed, _call_all, to be potentially
called from several locations within main.

This commit refactors the option processing code to simplify it and make
it easier to catch runtime errors in the script. This is done by
specializing the try-except block to only have an exception when the -p
argument is malformed. When the -p option is correctly selected by the
user, it calls a function in the unSub array directly, which will only
display one page of output. Finally, _call_all is only called from one
location within main.

Remove some commented out code.
Remove pages from output.

Pages seem to have been added into the output in the FreeNAS version of
the script. This patch removes pages from the output to more closely
resemble the freebsd version of the script.
Add a help option with usage information.
Force all lines to be shorter than 80 characters.