Merge branch 'selftests-bpf-test-sockmap-sockhash-redirection'

Michal Luczaj says:

====================
selftests/bpf: Test sockmap/sockhash redirection

The idea behind this series is to comprehensively test the BPF redirection:

BPF_MAP_TYPE_SOCKMAP,
BPF_MAP_TYPE_SOCKHASH
	x
	sk_msg-to-egress,
	sk_msg-to-ingress,
	sk_skb-to-egress,
	sk_skb-to-ingress
		x
		AF_INET, SOCK_STREAM,
		AF_INET6, SOCK_STREAM,
		AF_INET, SOCK_DGRAM,
		AF_INET6, SOCK_DGRAM,
		AF_UNIX, SOCK_STREAM,
		AF_UNIX, SOCK_DGRAM,
		AF_VSOCK, SOCK_STREAM,
		AF_VSOCK, SOCK_SEQPACKET

New module is introduced, sockmap_redir: all supported and unsupported
redirect combinations are tested for success and failure respectively. Code
is pretty much stolen/adapted from Jakub Sitnicki's sockmap_redir_matrix.c
[1].

Usage:
$ cd tools/testing/selftests/bpf
$ make
$ sudo ./test_progs -t sockmap_redir
...
Summary: 1/576 PASSED, 0 SKIPPED, 0 FAILED

[1]: https://github.com/jsitnicki/sockmap-redir-matrix/blob/main/sockmap_redir_matrix.c

Changes in v3:
- Drop unrelated changes; sockmap_listen, test_sockmap_listen, doc
- Collect tags [Jakub, John]
- Introduce BPF verdict programs especially for sockmap_redir [Jiayuan]
- Link to v2: https://lore.kernel.org/r/20250411-selftests-sockmap-redir-v2-0-5f9b018d6704@rbox.co

Changes in v2:
- Verify that the unsupported redirect combos do fail [Jakub]
- Dedup tests in sockmap_listen
- Cosmetic changes and code reordering
- Link to v1: https://lore.kernel.org/bpf/42939687-20f9-4a45-b7c2-342a0e11a014@rbox.co/
====================

Link: https://patch.msgid.link/20250515-selftests-sockmap-redir-v3-0-a1ea723f7e7e@rbox.co
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>