bpf: sync bpf.h to tools infrastructure

Pull in updates in BPF helper function description.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/include/uapi/linux/bpf.h

@@ -1466,8 +1466,8 @@ union bpf_attr {
  * 		If no cookie has been set yet, generate a new cookie. Once
  * 		generated, the socket cookie remains stable for the life of the
  * 		socket. This helper can be useful for monitoring per socket
- * 		networking traffic statistics as it provides a unique socket
- * 		identifier per namespace.
+ * 		networking traffic statistics as it provides a global socket
+ * 		identifier that can be assumed unique.
  * 	Return
  * 		A 8-byte long non-decreasing number on success, or 0 if the
  * 		socket field is missing inside *skb*.
@@ -1571,8 +1571,11 @@ union bpf_attr {
  * 		but this is only implemented for native XDP (with driver
  * 		support) as of this writing).
  *
- * 		All values for *flags* are reserved for future usage, and must
- * 		be left at zero.
+ * 		The lower two bits of *flags* are used as the return code if
+ * 		the map lookup fails. This is so that the return value can be
+ * 		one of the XDP program return codes up to XDP_TX, as chosen by
+ * 		the caller. Any higher bits in the *flags* argument must be
+ * 		unset.
  *
  * 		When used to redirect packets to net devices, this helper
  * 		provides a high performance increase over **bpf_redirect**\ ().