tools: bpf: synchronise BPF UAPI header with tools

Synchronise the bpf.h header under tools, to report the latest fixes and
additions to the documentation for the BPF helpers.
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>