Fix bug in stats_event_benchmark

Now, the number of elements in each simulated stats_event is correctly
sampled from a uniform distribution.

Rerunning the benchmarking tests indicates that truncating the buffer
increases the number of cycles require to log an event by only 1.6%.

Test: m libstatssocket_benchmark
Test: bit libstatssocket_benchmark:*
Change-Id: I8d5c1734861038beec8eeb7ce1f84a24bde25a75
diff --git a/libstats/socket/benchmark/stats_event_benchmark.cpp b/libstats/socket/benchmark/stats_event_benchmark.cpp
index b487c4d..9488168 100644
--- a/libstats/socket/benchmark/stats_event_benchmark.cpp
+++ b/libstats/socket/benchmark/stats_event_benchmark.cpp
@@ -22,7 +22,8 @@
     stats_event_set_atom_id(event, 100);
 
     // randomly sample atom size
-    for (int i = 0; i < rand() % 800; i++) {
+    int numElements = rand() % 800;
+    for (int i = 0; i < numElements; i++) {
         stats_event_write_int32(event, i);
     }