When performing make install in iproute2 (current git master),
if $(HAVE_MNL) is not selected, some Makefiles try to call
install with an empty target, which causes a non-critical make error.
Signed-off-by: Emeric Dupont <emeric.dupont@zii.aero>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>