Fix checkapi for OpenJDK 9 builds

This change explitly hides com.android.okhttp
from doclava. The public.txt generation was
previously relying on a package.html in
com.android to hide all subpackages, which
doesn't work with javadoc 9.

Test: make droid (with both OpenJDK 8 and OpenJDK 9)
Bug: 69709687
Change-Id: If61b69f913be044adb4cd34867459bde6330ea2c
diff --git a/Android.mk b/Android.mk
index f4a9ff9..b3db409 100644
--- a/Android.mk
+++ b/Android.mk
@@ -1027,6 +1027,7 @@
     -knowntags ./frameworks/base/docs/knowntags.txt \
     -knowntags ./libcore/known_oj_tags.txt \
     -manifest ./frameworks/base/core/res/AndroidManifest.xml \
+    -hidePackage com.android.okhttp \
     -hidePackage com.android.org.conscrypt \
     -since $(SRC_API_DIR)/1.xml 1 \
     -since $(SRC_API_DIR)/2.xml 2 \