net/sfc: use zero RSS channels as disabled RSS indicator

net/sfc: use zero RSS channels as disabled RSS indicator

Enabled RSS enables RSS hash computation and provision in pseudo header.
It still makes sense for applications even if only one Rx queue is used.

Fixes: 4ec1fc3ba881 ("net/sfc: add basic stubs for RSS support on driver attach")
Fixes: 088e17210a7a ("net/sfc: query RSS key and hash types config")
Fixes: 82faef507608 ("net/sfc: set RSS key and hash types config")
Fixes: af0d9317970c ("net/sfc: query RSS redirection table")
Fixes: 32bcfb0a50b1 ("net/sfc: update RSS redirection table")
Fixes: f5258439ee5d ("net/sfc: avoid failure on port start if Rx mode is rejected")

Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andy Moreton <amoreton@solarflare.com>