BUG/MINOR: activity/memprofile: reinitialize the free calls on DSO summary

BUG/MINOR: activity/memprofile: reinitialize the free calls on DSO summary

In commit 401fb0e87a ("MINOR: activity/memprofile: show per-DSO stats")
we added a summary per DSO. However the free calls/tot were not initialized
when creating a new entry because initially they were applied to any entry,
but since we don't update free calls for non-free capable callers, we still
need to reinitialize these entries when reassigning one. Because of this
bug, a "show profiling memory" output can randomly show highly negative
values on the DSO lines if it turns out that the DSO entry was created on
an alloc instead of a realloc/free.

Since the commit above was backported to 2.9, this one must go there as
well.