tools: Add ethtool.h header to tooling infra

This commit duplicates the ethtool.h file from the include/uapi/linux
directory in the kernel source to the tools/include/uapi/linux directory.

This action ensures that the ethtool.h file used in the tools directory
is in sync with the kernel's version, maintaining consistency across the
codebase.

There are some checkpatch warnings in this file that could be cleaned up,
but I preferred to move it over as-is for now to avoid disrupting the code.

Signed-off-by: Tushar Vyavahare <tushar.vyavahare@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/20240402114529.545475-2-tushar.vyavahare@intel.com