nfp: fix RSS hash key size when RSS is not supported

The nfp_net_get_rxfh_key_size() function returns -EOPNOTSUPP when
devices don't support RSS, and callers treat the negative value as a
large positive value since the return type is u32.

Return 0 when devices don't support RSS, aligning with the ethtool
interface .get_rxfh_key_size() that requires returning 0 in such cases.

Fixes: 9ff304b ("nfp: add support for reporting CRC32 hash function")
Signed-off-by: Kohei Enju <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: hyperenju

drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c

@@ -1788,7 +1788,7 @@ static u32 nfp_net_get_rxfh_key_size(struct net_device *netdev)
 	struct nfp_net *nn = netdev_priv(netdev);
 
 	if (!(nn->cap & NFP_NET_CFG_CTRL_RSS_ANY))
-		return -EOPNOTSUPP;
+		return 0;
 
 	return nfp_net_rss_key_sz(nn);
 }