ice: Fix persistent failure in ice_get_rxfh

Several ioctl functions have the ability to call ice_get_rxfh, however
all of these ioctl functions do not provide all of the expected
information in ethtool_rxfh_param. For example, ethtool_get_rxfh_indir does
not provide an rss_key. This previously caused ethtool_get_rxfh_indir to
always fail with -EINVAL.

This change draws inspiration from i40e_get_rss to handle this
situation, by only calling the appropriate rss helpers when the
necessary information has been provided via ethtool_rxfh_param.

Fixes: b66a972abb6b ("ice: Refactor ice_set/get_rss into LUT and key specific functions")
Signed-off-by: Cody Haas <[e-mail]>
Closes: https://lore.kernel.org/intel-wired-lan/[e-mail]/
Reviewed-by: Aleksandr Loktionov <[e-mail]>
Reviewed-by: Przemek Kitszel <[e-mail]>
Tested-by: Rinitha S <[e-mail]> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <[e-mail]>

drivers/net/ethernet/intel/ice/ice.h

···
 int
 ice_xdp_xmit(struct net_device *dev, int n, struct xdp_frame **frames,
 	     u32 flags);
+int ice_get_rss(struct ice_vsi *vsi, u8 *seed, u8 *lut, u16 lut_size);
 int ice_set_rss_lut(struct ice_vsi *vsi, u8 *lut, u16 lut_size);
 int ice_get_rss_lut(struct ice_vsi *vsi, u8 *lut, u16 lut_size);
 int ice_set_rss_key(struct ice_vsi *vsi, u8 *seed);

drivers/net/ethernet/intel/ice/ice_ethtool.c

···
 	if (!lut)
 		return -ENOMEM;
 
-	err = ice_get_rss_key(vsi, rxfh->key);
-	if (err)
-		goto out;
-
-	err = ice_get_rss_lut(vsi, lut, vsi->rss_table_size);
+	err = ice_get_rss(vsi, rxfh->key, lut, vsi->rss_table_size);
 	if (err)
 		goto out;
 

drivers/net/ethernet/intel/ice/ice_main.c

···
 }
 
 /**
+ * ice_get_rss - Get RSS LUT and/or key
+ * @vsi: Pointer to VSI structure
+ * @seed: Buffer to store the key in
+ * @lut: Buffer to store the lookup table entries
+ * @lut_size: Size of buffer to store the lookup table entries
+ *
+ * Return: 0 on success, negative on failure
+ */
+int ice_get_rss(struct ice_vsi *vsi, u8 *seed, u8 *lut, u16 lut_size)
+{
+	int err;
+
+	if (seed) {
+		err = ice_get_rss_key(vsi, seed);
+		if (err)
+			return err;
+	}
+
+	if (lut) {
+		err = ice_get_rss_lut(vsi, lut, lut_size);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+/**
  * ice_set_rss_hfunc - Set RSS HASH function
  * @vsi: Pointer to VSI structure
  * @hfunc: hash function (ICE_AQ_VSI_Q_OPT_RSS_*)