Merge branch 'bpf-sk-msg-pop-data'

Merge branch 'bpf-sk-msg-pop-data'

John Fastabend says:

====================
After being able to add metadata to messages with sk_msg_push_data we
have also found it useful to be able to "pop" this metadata off before
sending it to applications in some cases. This series adds a new helper
sk_msg_pop_data() and the associated patches to add tests and tools/lib
support.

Thanks!

v2: Daniel caught that we missed adding sk_msg_pop_data to the changes
    data helper so that the verifier ensures BPF programs revalidate
    data after using this helper. Also improve documentation adding a
    return description and using RST syntax per Quentin's comment. And
    delta calculations for DROP with pop'd data (albeit a strange set
    of operations for a program to be doing) had potential to be
    incorrect possibly confusing user space applications, so fix it.
====================

Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>