bnxt_en: Fix ethtool -S statitics with XDP or TCs enabled.

We are returning the wrong count for ETH_SS_STATS in get_sset_count()
when XDP or TCs are enabled.  In a recent commit, we got rid of
irrelevant counters when the ring is RX only or TX only, but we
did not make the proper adjustments for the count.  As a result,
when we have XDP or TCs enabled, we are returning an excess count
because some of the rings are TX only.  This causes ethtool -S to
display extra counters with no counter names.

Fix bnxt_get_num_ring_stats() by not assuming that all rings will
always have RX and TX counters in combined mode.

Fixes: 125592fb

 ("bnxt_en: show only relevant ethtool stats for a TX or RX ring")
Reviewed-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>