bnxt_en: don't update cpr->rx_bytes with uninitialized length len

Currently in the cases where cmp_type == CMP_TYPE_RX_L2_TPA_START_CMP or
CMP_TYPE_RX_L2_TPA_END_CMP the exit path updates cpr->rx_bytes with an
uninitialized length len.  Fix this by adding a new exit path that does
not update the cpr stats with the bogus length len and remove the unused
label next_rx_no_prod.

Detected by CoverityScan, CID#1463807 ("Uninitialized scalar variable")
Fixes: 6a8788f2 ("bnxt_en: add support for software dynamic interrupt moderation")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>