statsd: mark libstats_jni as jni_libs

This helps the build system to convey the information to linkerconfig so
that jni_libs are available via libnativeloader.

Bug: 150767721
Test: presubmit
Merged-In: Ie32e88355828c8f696cce9d128eebb6da70026f1
Change-Id: Ie32e88355828c8f696cce9d128eebb6da70026f1
(cherry picked from commit 95642bbc)