bpf/selftests: Add check for updating XDP bpf_link with wrong program type

Add a check to the xdp_link selftest that the kernel rejects replacing an
XDP program with a different program type on link update.

v2:
- Split this out into its own patch.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/20220107221115.326171-3-toke@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: Normalize XDP section names in selftests

Convert almost all SEC("xdp_blah") uses to strict SEC("xdp") to comply
with strict libbpf 1.0 logic of exact section name match for XDP program
types. There is only one exception, which is only tested through
iproute2 and defines multiple XDP programs within the same BPF object.
Given iproute2 still works in non-strict libbpf mode and it doesn't have
means to specify XDP programs by its name (not section name/title),
leave that single file alone for now until iproute2 gains lookup by
function/program name.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/bpf/20210928161946.2512801-3-andrii@kernel.org

selftests/bpf: Add BPF XDP link selftests

Add selftest validating all the attachment logic around BPF XDP link. Test
also link updates and get_obj_info() APIs.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200722064603.3350758-9-andriin@fb.com