net/mlx5e: Update netdev features only after a successful ringparam set

mlx5 couples HW-GRO with tcp-data-split. If a user sets rx-gro-hw on ->
tcp-data-split on -> rx-gro-hw off, the driver will leave HW-GRO on.
mlx5e_ethtool_set_tcp_data_split() calls netdev_update_features() when
tcp-data-split goes from enabled to disabled in case HW-GRO needs to be
released. mlx5e_fix_features() reads the new HDS config from
dev->cfg_pending, so HW-GRO is released before all ring parameters are
validated.

If the subsequent call to mlx5e_ethtool_set_ringparam() fails, the
ethtool core discards the pending change and reports tcp-data-split
enabled. The device is no longer splitting, and subsequent ring changes
are blocked.

Move the call to netdev_update_features() after
mlx5e_ethtool_set_ringparam() exits successfully.

The issue was discovered by manual code inspection during review of
a change that stops mlx5 users from disabling tcp-data-split. It was
reproduced on a ConnectX-7 with ethtool alone.

Steps to reproduce:
ethtool -K eth0 rx-gro-hw on
ethtool -G eth0 tcp-data-split on
ethtool -K eth0 rx-gro-hw off # HW-GRO kept on for tcp-data-split

ethtool -G eth0 tcp-data-split off rx 1 # de-sync driver & kernel state
 netlink error: mlx5_core: rx (1) < min (16)
 netlink error: Invalid argument

ethtool -G eth0 rx 1024 # valid ring changes are now blocked
 netlink error: mlx5_core: TCP-data-split is not supported when GRO HW is disabled
 netlink error: Invalid argument

This is not a terminal state, users can recover by setting rx-gro-hw on.
With the fix, the failing ringparam set leaves rx-gro-hw on and later
ring changes succeed.

Fixes: 46bcce5dfd33 ("net/mlx5e: Support ethtool tcp-data-split settings")
Reported-by: Björn Töpel <bjorn@kernel.org>
Closes: https://lore.kernel.org/87se2grw3d.fsf@all.your.base.are.belong.to.us/
Signed-off-by: Dimitri Daskalakis <daskald@meta.com>
Reviewed-by: Björn Töpel <bjorn@kernel.org>
Reviewed-by: Nimrod Oren <noren@nvidia.com>
Acked-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20261017005401.1582755-1-dimitri.daskalakis1@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>