ovs-ivshm-mngr: always share main mempool

Make the ovs-ivshm-mngr app always sharing the main mempool with IVSHM
clients too (KNI clients already needed this DPDK object). Solves a
segfault error that will occur if the client app tries to modify
the packets content (mbufs). Mbufs reside in the mempool address
space which is not being shared/mapped into the client.

Change-Id: I9ed9b68f366d3e2b3c71d7493a8d336c812bc21f
Signed-off-by: Nicolas Pernas Maradei <nicolasx.pernas.maradei@intel.com>
Reviewed-by: Mark D. Gray <mark.d.gray@intel.com>