net: sched: pkt_cls: remove unused macros from uapi

Jamal points out that this header also contains kernel internal magic that
cannot be used from userspace for anything meaningful.

Lets remove what the kernel doesn't use anymore and wrap remainder with
__KERNEL__.

Suggested-by: Jamal Hadi Salim <jhs@mojatatu.com>
Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>