bnxt: add pause frame stats

These stats are already reported in ethtool -S.
Michael confirms they are equivalent to standard stats.

v2: - fix sparse warning about endian by using the macro
    - use u64 for pointer type

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>