bnxt_en: Clear TPA flags when BNXT_FLAG_NO_AGG_RINGS is set.

Commit bdbd1eb5 ("bnxt_en: Handle no aggregation ring gracefully.")
introduced the BNXT_FLAG_NO_AGG_RINGS flag.  For consistency,
bnxt_set_tpa_flags() should also clear TPA flags when there are no
aggregation rings.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>