Fixes memory leak when drop_stat messages processed

This patch fix a memory leak when drop stats messages
are processed. A temp alloc for aggregation was not freed.

Change-Id: I2f5991fc555843af87b43aec7662d384e6b74f9d
Closes-bug: #1373026
(cherry picked from commit b85be29d57fae111c9c6f3ded025d0a3c2145900)