net/udpgso_bench.sh add UDP GSO audit tests

net/udpgso_bench.sh add UDP GSO audit tests

Audit tests count the total number of messages sent and compares
with total number of CMSG received on error queue. Example:

    udp gso zerocopy timestamp audit
    udp rx:   1599 MB/s  1166414 calls/s
    udp tx:   1615 MB/s    27395 calls/s  27395 msg/s
    udp rx:   1634 MB/s  1192261 calls/s
    udp tx:   1633 MB/s    27699 calls/s  27699 msg/s
    udp rx:   1633 MB/s  1191358 calls/s
    udp tx:   1631 MB/s    27678 calls/s  27678 msg/s
    Summary over 4.000 seconds...
    sum udp tx:   1665 MB/s      82772 calls (27590/s)      82772 msgs (27590/s)
    Tx Timestamps:               82772 received                 0 errors
    Zerocopy acks:               82772 received

Errors are thrown if CMSG count does not equal send count,
example:

    Summary over 4.000 seconds...
    sum tcp tx:   7451 MB/s     493706 calls (123426/s)     493706 msgs (123426/s)
    ./udpgso_bench_tx: Unexpected number of Zerocopy completions:    493706 expected    493704 received

Also reduce individual test time from 4 to 3 seconds so that
overall test time does not increase significantly.

v3: Enhancements as per Willem de Bruijn <willemb@google.com>
    - document -P option for TCP audit

Signed-off-by: Fred Klassen <fklassen@appneta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>