net/sfc: fix TSO limits imposed to the number of Tx queues

net/sfc: fix TSO limits imposed to the number of Tx queues

The number of Tx queues requested by the user must not be overridden;
instead, the limits imposed by TSO must be applied to the advertised
maximum

Fixes: fec33d5bb3eb ("net/sfc: support firmware-assisted TSO")
Cc: stable@dpdk.org
Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andrew Lee <alee@solarflare.com>
Reviewed-by: Andy Moreton <amoreton@solarflare.com>