d/rules: properly enable dpdk systemd service

d/rules: properly enable dpdk systemd service

Since ca40d310 "Convert debian/rules to new style DH targets" the
installed service is by default disabled which is not intended.

Add --with=systemd to dh, to issue the right sequence and be safe
against future changes in that regard.

Change-Id: I3d8be98397e59a3cc295368bf99fdf343d38419d
Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
(cherry picked from commit f27802a43419139be089eb7eccd7edac0e59daf4)
Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>