net: remove IFF_* re-definition

We re-define values of enum netdev_priv_flags as preprocessor
macros with the same name. I guess this was done to avoid breaking
out of tree modules which may use #ifdef X for kernel compatibility?
Commit 7aa98047 ("net: move net_device priv_flags out from UAPI")
which added the enum doesn't say. In any case, the flags with defines
are quite old now, and defines for new flags don't get added.
OOT drivers have to resort to code greps for compat detection, anyway.
Let's delete these defines, save LoC, help LXR link to the right place.

Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://patch.msgid.link/20240801163401.378723-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>