net: add UAPI to the header guard in various network headers

net: add UAPI to the header guard in various network headers

fib_rule, ip6_tunnel, and a whole lot of if_* headers lack the customary
_UAPI in the header guard. Without it YNL build can't protect from in tree
and system headers both getting included. YNL doesn't need most of these
but it's annoying to have to fix them one by one.

Note that header installation strips this _UAPI prefix so this should
result in no change to the end user.

Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20250416200840.1338195-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>