Merge branch 'use-network-helpers-part-7'

Geliang Tang says:

====================
use network helpers, part 7

From: Geliang Tang <tanggeliang@kylinos.cn>

v6:
 - update ASSERT strings in patch 4 as Eduard suggested. (thanks)

v5:
 - update patch 1, add getsockopt(SO_PROTOCOL) in connect_to_fd() to
fix errors reported by CI.

v4:
 - fix errors reported by CI.

v3:
 - rename start_client to client_socket
 - Use connect_to_addr in connect_to_fd_opt

v2:
 - update patch 2, extract a new helper start_client.
 - drop patch 3, keep must_fail in network_helper_opts.

Drop type and noconnect from network_helper_opts. And use start_server_str
in mptcp and test_tcp_check_syncookie_user.

Patches 1-4 address Martin's comments in the previous series.
====================

Link: https://lore.kernel.org/r/cover.1718932493.git.tanggeliang@kylinos.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>