srm: Clean up srmLs request implementation

Mostly cosmetical to bring the code in line with other request
implementations.

Changed the value of srm.limits.request.ls.levels.max to infinity.
This is to make the default values be spec compliant.

Target: trunk
Require-notes: yes
Require-book: yes
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/6144/