net/sfc: avoid Tx queue setup failure if thresholds are set

net/sfc: avoid Tx queue setup failure if thresholds are set

Tx queue prefetch, host and writeback thresholds are used for
performance fine-tuning and not applicable to Solarflare NICs.
It is safe to just log warning and do not fail Tx queue setup
to be more friendly to DPDK applications which hardcode it.

Fixes: b1b7ad933b39 ("net/sfc: set up and release Tx queues")
Cc: stable@dpdk.org
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>