devlink: Fix length of eswitch inline-mode

Set eswitch inline-mode to be u8, not u16. Otherwise, errors below

$ devlink dev eswitch set pci/0000:08:00.0 mode switchdev \
  inline-mode network
    Error: Attribute failed policy validation.
    kernel answers: Numerical result out of rang
    netlink: 'devlink': attribute type 26 has an invalid length.

Fixes: f2f9dd16

 ("netlink: specs: devlink: add the remaining command to generate complete split_ops")
Signed-off-by: William Tu <witu@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240310164547.35219-1-witu@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>