Add -Wshadow to bpf_cc_defaults

Test: m
Change-Id: I08899d0c1bbdb05c3a2ef7df4b0debe748c25d94
diff --git a/Android.bp b/Android.bp
index 023ab6f..fd5b5cf 100644
--- a/Android.bp
+++ b/Android.bp
@@ -48,6 +48,7 @@
         "-Werror=sometimes-uninitialized",
         "-Wextra",
         "-Wnullable-to-nonnull-conversion",
+        "-Wshadow",
         "-Wsign-compare",
         "-Wtautological-unsigned-zero-compare",
         "-Wthread-safety",