net/bnxt: workaround spurious zero stats in Thor

net/bnxt: workaround spurious zero stats in Thor

There is a HW bug that can result in certain stats being reported as
zero.
Workaround this by ignoring stats with a value of zero based on the
previously stored snapshot of the same stat.
This bug mainly manifests in the output of func_qstats as FW aggregrates
each ring's stat value to give the per function stat and if one of
them is zero, the per function stat value ends up being lower than the
previous snapshot which shows up as a zero PPS value in testpmd.
Eliminate invocation of func_qstats and aggregate the per-ring stat
values in the driver itself to derive the func_qstats output post
accounting for the spurious zero stat value.

Bugzilla ID: 641
Fixes: f8168ca0e690 ("net/bnxt: support thor controller")
Cc: stable@dpdk.org
Signed-off-by: Somnath Kotur <somnath.kotur@broadcom.com>
Reviewed-by: Lance Richardson <lance.richardson@broadcom.com>
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Acked-by: Ajit Khaparde <ajit.khaparde@broadcom.com>