Add module dpif-netdev-perf to host all PMD performance-related
data structures and functions in dpif-netdev. Refactor the PMD
stats handling in dpif-netdev and delegate whatever possible into
the new module, using clean interfaces to shield dpif-netdev from
the implementation details. Accordingly, the all PMD statistics
members are moved from the main struct dp_netdev_pmd_thread into
a dedicated member of type struct pmd_perf_stats.

Include Darrel's prior refactoring of PMD stats contained in
[PATCH v5,2/3] dpif-netdev: Refactor some pmd stats:

1. The cycles per packet counts are now based on packets
received rather than packet passes through the datapath.

2. Packet counters are now kept for packets received and
packets recirculated. These are kept as separate counters for
maintainability reasons. The cost of incrementing these counters
is negligible.  These new counters are also displayed to the user.

3. A display statistic is added for the average number of
datapath passes per packet. This should be useful for user
debugging and understanding of packet processing.

4. The user visible 'miss' counter is used for successful upcalls,
rather than the sum of sucessful and unsuccessful upcalls. Hence,
this becomes what user historically understands by OVS 'miss upcall'.
The user display is annotated to make this clear as well.

5. The user visible 'lost' counter remains as failed upcalls, but
is annotated to make it clear what the meaning is.

6. The enum pmd_stat_type is annotated to make the usage of the
stats counters clear.

7. The subtable lookup stats is renamed to make it clear that it
relates to masked lookups.

8. The PMD stats test is updated to handle the new user stats of
packets received, packets recirculated and average number of datapath
passes per packet.

On top of that introduce a "-pmd <core>" option to the PMD info
commands to filter the output for a single PMD.

Made the pmd-stats-show output a bit more readable by adding a blank
between colon and value.

Signed-off-by: Jan Scheurich <jan.scheurich@ericsson.com>
Co-authored-by: Darrell Ball <dlu998@gmail.com>
Signed-off-by: Darrell Ball <dlu998@gmail.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>
Acked-by: Billy O'Mahony <billy.o.mahony@intel.com>
Signed-off: Ian Stokes <ian.stokes@intel.com>