oxenstored: comments explaining some variables

oxenstored: comments explaining some variables

It took a while of reading and reasoning to work out what these are
for, so here are comments to make life easier for everyone reading
this code in future.

Reported-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Thomas Sanders <thomas.sanders@citrix.com>
Reviewed-by: Jonathan Davies <jonathan.davies@citrix.com>
Reviewed-by: Ian Jackson <ian.jackson@eu.citrix.com>
Reviewed-by: Christian Lindig <christian.lindig@citrix.com>