ethtool: Fix context creation with no parameters

ethtool: Fix context creation with no parameters

The 'at least one change' requirement is not applicable for context
creation, skip the check in such case.
This allows a command such as 'ethtool -X eth0 context new' to work.

The command works by mistake when using older versions of userspace
ethtool due to an incompatibility issue where rxfh.input_xfrm is passed
as zero (unset) instead of RXH_XFRM_NO_CHANGE as done with recent
userspace. This patch does not try to solve the incompatibility issue.

Link: https://lore.kernel.org/netdev/05ae8316-d3aa-4356-98c6-55ed4253c8a7@nvidia.com/
Fixes: 84a1d9c48200 ("net: ethtool: extend RXNFC API to support RSS spreading of filter matches")
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Jianbo Liu <jianbol@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Edward Cree <ecree.xilinx@gmail.com>
Link: https://patch.msgid.link/20240807173352.3501746-1-gal@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>