octeontx2-af: Harden rule validation.

Accept TC offload classifier rule only if SPI field
can be extracted by HW.

Signed-off-by: Ratheesh Kannoth <rkannoth@marvell.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>