sfc: Correct comment about number of TX queues used on EF10

EF10 implements option descriptors to switch TX checksum offload
on and off between packets.  We could therefore use a single
hardware TX queue per kernel TX queue, although we don't yet.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Shradha Shah <sshah@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>