tools/xenstored: liveupdate: Increase the maximum number of parameters

tools/xenstored: liveupdate: Increase the maximum number of parameters

The longest possible command line for LiveUpdate is:

  liveupdate -s -t <timeout> -F

This is 5 parameters. However, the maximum is currently specified to 4.
This means the some of the parameters will get ignored.

Update the field max_pars to 5 so and admin can specify the timeout and
force at the same time.

Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Release-Acked-by: Ian Jackson <iwj@xenproject.org>