nfp: ethtool: fix the bug of setting unsupported port speed

nfp: ethtool: fix the bug of setting unsupported port speed

[ Upstream commit d9c1f5538fac1d9085e9f597529c16fba37510c2 ]

Unsupported port speed can be set and cause error. Now fixing it
and return an error if setting unsupported speed.

This fix depends on the following, which was included in v6.2-rc1:
commit 6febe7c3af75 ("nfp: ethtool: support reporting link modes").

Fixes: 6d7e9e5ded66 ("nfp: add support for .set_link_ksettings()")
Signed-off-by: Yu Xiao <yu.xiao@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>