examples/l3fwd-power: fix early shutdown

examples/l3fwd-power: fix early shutdown

Currently, EAL init cannot be interrupted with SIGINT because the
signal handler is already overridden by the time EAL init happens.

Fix it by moving signal handler installation to after EAL
initialization, to allow SIGNIT to interrupt EAL initialization.

Fixes: d7937e2e3d12 ("power: initial import")
Fixes: 613ce6691c0d ("examples/l3fwd-power: implement proper shutdown")
Cc: stable@dpdk.org
Signed-off-by: Harneet Singh <harneet.singh@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>