tools: bpf: synchronise BPF UAPI header with tools

Synchronise the bpf.h header under tools, to report the fixes and
additions recently brought to the documentation for the BPF helpers.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>