Merge branch 'bpf-msg-push-data'

John Fastabend says:

====================
This series adds a new helper bpf_msg_push_data to be used by
sk_msg programs. The helper can be used to insert extra bytes into
the message that can then be used by the program as metadata tags
among other things.

The first patch adds the helper, second patch the libbpf support,
and last patch updates test_sockmap to run msg_push_data tests.

v2: rebase after queue map and in filter.c convert int -> u32
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>