DO NOT MERGE: Revert "remove external/libnl-headers from the manifest"

This reverts commit fd1e90b3b1455615ff00c21dc90a0d4bfa21840e.

libnl_2 needs to stay in AOSP for now for compatibility with
GPL test builds.

(cherry picked from commit 65480a071f2f0db010d47535513a98e47477d8d2)

Change-Id: Ide26ec95bb606165094890faa7d3aee7490be7f6
1 file changed