ixgbe: Allow flow hash to be set via ethtool

ixgbe currently returns `EINVAL` whenever the flowhash it set by ethtool
because the ethtool code in the kernel passes a non-zero value for hfunc
that ixgbe should allow.

When ethtool is called with `ETHTOOL_SRXFHINDIR`,
`ethtool_set_rxfh_indir` will call ixgbe's set_rxfh function
with `ETH_RSS_HASH_NO_CHANGE`. This value should be accepted.

When ethtool is called with `ETHTOOL_SRSSH`, `ethtool_set_rxfh` will
call ixgbe's set_rxfh function with `rxfh.hfunc`, which appears to be
hardcoded in ixgbe to always be `ETH_RSS_HASH_TOP`. This value should
also be accepted.

Before this patch:

$ sudo ethtool -L eth1 combined 10
$ sudo ethtool -X eth1 default
Cannot set RX flow hash configuration: Invalid argument

After this patch:

$ sudo ethtool -L eth1 combined 10
$ sudo ethtool -X eth1 default
$ sudo ethtool -x eth1
RX flow hash indirection table for eth1 with 10 RX ring(s):
    0:      0     1     2     3     4     5     6     7
    8:      8     9     0     1     2     3     4     5
   16:      6     7     8     9     0     1     2     3
   24:      4     5     6     7     8     9     0     1
   ...

Fixes: 1c7cf078 ("ixgbe: support for ethtool set_rxfh")
Signed-off-by: Joe Damato <jdamato@fastly.com>
Reviewed-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c

@@ -3131,8 +3131,8 @@ static int ixgbe_set_rxfh(struct net_device *netdev, const u32 *indir,
 	int i;
 	u32 reta_entries = ixgbe_rss_indir_tbl_entries(adapter);
 
-	if (hfunc)
-		return -EINVAL;
+	if (hfunc != ETH_RSS_HASH_NO_CHANGE && hfunc != ETH_RSS_HASH_TOP)
+		return -EOPNOTSUPP;
 
 	/* Fill out the redirection table */
 	if (indir) {