netdev-dpdk: fix port addition for ports sharing same PCI id

netdev-dpdk: fix port addition for ports sharing same PCI id

Some NICs have only one PCI address associated with multiple ports. This
patch extends the dpdk-devargs option's format to cater for such devices.

To achieve that, this patch uses a new syntax that will be adapted and
implemented in future DPDK release (likely, v18.05):
    http://dpdk.org/ml/archives/dev/2017-December/084234.html

And since it's the DPDK duty to parse the (complete and full) syntax
and this patch is more likely to serve as an intermediate workaround,
here I take a simpler and shorter syntax from it (note it's allowed to
have only one category being provided):
    class=eth,mac=00:11:22:33:44:55:66

Also, old compatibility is kept. Users can still go on with using the
PCI id to add a port (if that's enough for them). Meaning, this patch
will not break anything.

This patch is basically based on the one from Ciara:
    https://mail.openvswitch.org/pipermail/ovs-dev/2017-October/339496.html

Cc: Loftus Ciara <ciara.loftus@intel.com>
Cc: Thomas Monjalon <thomas@monjalon.net>
Cc: Kevin Traynor <ktraynor@redhat.com>
Signed-off-by: Yuanhan Liu <yliu@fridaylinux.org>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>