bpf: sync bpf.h to tools infrastructure

 * 		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*.

 * 		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**\ ().