statistics about index lookup report a wrong duration

[tbordaz]

Issue Description
When nsslapd-statlog-level is set to '1' it reports statistics about indexes lookup. A statistic is the duration of the lookup. This duration is wrong as it only reports the duration of the last index lookup.
Indeed, a filter contains several components and the duration should be displayed for each of them.

Package Version and Platform:

• since 2.4 ( RFE Extend log of operations statistics in access log #3729)

Steps to Reproduce
Steps to reproduce the behavior:
set nsslapd-statlog-level=1 and do a search with multiple components. check that a single duration is reported

Expected results
We should report a duration per component