Add type cast to fix build error with "-Wsign-compare" cflag.

There is build error if "-Wsign-compare" is defined in cflags.
Also add "-Wsign-compare" to Android.bp

Test: Build

Change-Id: If41da96ec521a0d2dcddf660e7effa218c99810d
Signed-off-by: Sehee Park <sehee32.park@samsung.com>
diff --git a/tests/benchmarks/bpf_benchmark.cpp b/tests/benchmarks/bpf_benchmark.cpp
index 6ee83cb..c7d518d 100644
--- a/tests/benchmarks/bpf_benchmark.cpp
+++ b/tests/benchmarks/bpf_benchmark.cpp
@@ -33,7 +33,7 @@
 }
 
 BENCHMARK_DEFINE_F(BpfBenchMark, MapUpdateEntry)(benchmark::State& state) {
-    for (int i = 0; i < TEST_MAP_SIZE; i++) {
+    for (uint32_t i = 0; i < TEST_MAP_SIZE; i++) {
         expectOk(mBpfTestMap.writeValue(i, i, BPF_NOEXIST));
     }
     for (auto _ : state) {
@@ -42,7 +42,7 @@
 }
 
 BENCHMARK_DEFINE_F(BpfBenchMark, MapDeleteAddEntry)(benchmark::State& state) {
-    for (int i = 0; i < TEST_MAP_SIZE; i++) {
+    for (uint32_t i = 0; i < TEST_MAP_SIZE; i++) {
         expectOk(mBpfTestMap.writeValue(i, i, BPF_NOEXIST));
     }
     for (auto _ : state) {