build: fix error in include/Makefile.am

Just introduced by me, as an oversight from commit
11f9cc0914aef697c1f49bca7353117cb65fd318.

Signed-off-by: Thomas Haller <thaller@redhat.com>
libnl-3.2.25-rc1 release

Signed-off-by: Thomas Haller <thaller@redhat.com>