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.

Change-Id: I85365fb4b8931a998e564d30800a06343a47fdd8
1 file changed