dpif-netdev: Log rxq assignment for isolated pmd.

dpif-netdev: Log rxq assignment for isolated pmd.

There is no log about isolated rxq assignment in a pmd today, which
sometimes could be useful to trace rxq/pmd pinning, when debugging
with log. Ovs-appctl dpif-netdev/pmd-rxq-show reports about it
already, but logging is helpful to trace pinning in time.

Signed-off-by: Gowrishankar Muthukrishnan <gmuthukr@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>