dpif-netdev: Add percentage of pmd/core used by each rxq.

dpif-netdev: Add percentage of pmd/core used by each rxq.

It is based on the length of history that is stored about an
rxq (currently 1 min).

$ ovs-appctl dpif-netdev/pmd-rxq-show
pmd thread numa_id 0 core_id 4:
        isolated : false
        port: dpdkphy1         queue-id:  0    pmd usage: 70 %
        port: dpdkvhost0       queue-id:  0    pmd usage:  0 %
pmd thread numa_id 0 core_id 6:
        isolated : false
        port: dpdkphy0         queue-id:  0    pmd usage: 64 %
        port: dpdkvhost1       queue-id:  0    pmd usage:  0 %

These values are what would be used as part of rxq to pmd
assignment due to a reconfiguration event e.g. adding pmds,
adding rxqs or with the command:

ovs-appctl dpif-netdev/pmd-rxq-rebalance

Signed-off-by: Jan Scheurich <jan.scheurich@ericsson.com>
Co-authored-by: Jan Scheurich <jan.scheurich@ericsson.com>
Signed-off-by: Kevin Traynor <ktraynor@redhat.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>