mbuf: use default mempool handler from config

mbuf: use default mempool handler from config

By default, the mempool ops used for mbuf allocations is a multi
producer and multi consumer ring. We could imagine a target (maybe some
network processors?) that provides an hardware-assisted pool
mechanism. In this case, the default configuration for this architecture
would contain a different value for RTE_MBUF_DEFAULT_MEMPOOL_OPS.

Signed-off-by: David Hunt <david.hunt@intel.com>
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Reviewed-by: Jan Viktorin <viktorin@rehivetech.com>
Acked-by: Shreyansh Jain <shreyansh.jain@nxp.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>