Follow-up to r1606770.

* subversion/tests/cmdline/svnadmin_tests.py
  (FSFS_Index.modify_item): LEN shall also be in HEX.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1606801 13f79535-47bb-0310-9956-ffa450edef68