build: Updating LOCAL_MODULE_TAGS with optional tag

Change-Id: I3ef2d50800e08389c303e28f2237c4eb8e1bc0e9
CRs-Fixed: 310616
diff --git a/src/Android.mk b/src/Android.mk
index 0b58559..c62575a 100644
--- a/src/Android.mk
+++ b/src/Android.mk
@@ -4,6 +4,8 @@
 
 LOCAL_MODULE    := libbson
 
+LOCAL_MODULE_TAGS := optional
+
 LOCAL_SRC_FILES := bson.c numbers.c
 
 LOCAL_CFLAGS := -DMONGO_HAVE_STDINT