net: ethtool: Fix symmetric-xor RSS RX flow hash check

net: ethtool: Fix symmetric-xor RSS RX flow hash check

Commit 13e59344fb9d ("net: ethtool: add support for symmetric-xor RSS hash")
adds a check to the ethtool set_rxnfc operation, which checks the RX
flow hash if the flag RXH_XFRM_SYM_XOR is set. This flag is introduced
with the same commit. It calls the ethtool get_rxfh operation to get the
RX flow hash data. If get_rxfh is not supported, then EOPNOTSUPP is
returned.

There are driver like tsnep, macb, asp2, genet, gianfar, mtk, ... which
support the ethtool operation set_rxnfc but not get_rxfh. This results
in EOPNOTSUPP returned by ethtool_set_rxnfc() without actually calling
the ethtool operation set_rxnfc. Thus, set_rxnfc got broken for all
these drivers.

Check RX flow hash in ethtool_set_rxnfc() only if driver supports RX
flow hash.

Fixes: 13e59344fb9d ("net: ethtool: add support for symmetric-xor RSS hash")
Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Reviewed-by: Ravi Gunasekaran <r-gunasekaran@ti.com>
Link: https://lore.kernel.org/r/20231226205536.32003-1-gerhard@engleder-embedded.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>