Merge branch 'Add _opts variant for bpf_*_get_fd_by_id()'

Merge branch 'Add _opts variant for bpf_*_get_fd_by_id()'

Roberto Sassu says:

====================
From: Roberto Sassu <roberto.sassu@huawei.com>

Add the _opts variant for bpf_*_get_fd_by_id() functions, to be able to
pass to the kernel more options, when requesting a fd of an eBPF object.

Pass the options through a newly introduced structure,
bpf_get_fd_by_id_opts, which currently contains open_flags (the other two
members are for compatibility and for padding).

open_flags allows the caller to request specific permissions to access a
map (e.g. read-only). This is useful for example in the situation where a
map is write-protected.

Besides patches 2-6, which introduce the new variants and the data
structure, patch 1 fixes the LIBBPF_1.0.0 declaration in libbpf.map.

Changelog

v1:
 - Don't CC stable kernel mailing list for patch 1 (suggested by Andrii)
 - Rename bpf_get_fd_opts struct to bpf_get_fd_by_id_opts (suggested by
   Andrii)
 - Move declaration of _opts variants after non-opts variants (suggested by
   Andrii)
 - Correctly initialize bpf_map_info, fix style issues, use map from
   skeleton, check valid fd in the test (suggested by Andrii)
 - Rename libbpf_get_fd_opts test to libbpf_get_fd_by_id_opts
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>