app/testpmd: add multiple pools per core creation

app/testpmd: add multiple pools per core creation

The command line parameter --mbuf-size is updated, it can handle
the multiple values like the following:

--mbuf-size=2176,512,768,4096

specifying the creation the extra memory pools with the requested
mbuf data buffer sizes. If some buffer split feature is engaged
the extra memory pools can be used to configure the Rx queues
with rte_the_dev_rx_queue_setup_ex().

The extra pools are created with requested sizes, and pool names
are assigned with appended index: mbuf_pool_socket_%socket_%index.
Index zero is used to specify the first mandatory pool to maintain
compatibility with existing code.

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>