srm: Fix cut'n'paste error in request history period configuration

Addresses premature garbage collection of put requests.

Target: trunk
Request: 2.7
Require-notes: no
Require-book: no
Acked-by: Dmitry Litvintsev <litvinse@fnal.gov>
Patch: http://rb.dcache.org/r/5930/
(cherry picked from commit dcec5dab99e62e0c488889e3b452397bc9ce57c2)
Merge pull request #172 from gbehrmann/fix/2.7/rb5930

srm: Fix cut'n'paste error in request history period configuration