bpf: remove SK_REDIRECT from UAPI

Now that SK_REDIRECT is no longer a valid return code. Remove it
from the UAPI completely. Then do a namespace remapping internal
to sockmap so SK_REDIRECT is no longer externally visible.

Patchs primary change is to do a namechange from SK_REDIRECT to
__SK_REDIRECT

Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/bpf.h

@@ -788,7 +788,6 @@ struct xdp_md {
 enum sk_action {
 	SK_DROP = 0,
 	SK_PASS,
-	SK_REDIRECT,
 };
 
 #define BPF_TAG_SIZE	8