Apply two cleanups suggested by Stanislav and bobby on the original
selftest series:

- Reorder local variable declarations into reverse christmas-tree
  order (longest line first). Because that ordering puts socklen_t
  optlen before the variable whose size it stores, the
  "optlen = sizeof(...)" initializer is moved out of the declaration
  to a plain assignment in the test body, as Stanislav suggested.

- Add ASSERT_EQ(optlen, ...) on every error path so the value the
  kernel writes back to the userspace optlen is pinned down even
  when the syscall returns -1. With do_sock_getsockopt() now writing
  opt->optlen back to userspace unconditionally, asserting that the
  netlink/vsock error paths leave the original input length untouched
  guards against future regressions.

Bobby Eshleman pointed out that
SO_VM_SOCKETS_CONNECT_TIMEOUT_NEW/OLD return a sock_timeval-shaped
payload (16 bytes on 64-bit), which is wider than the u64 case
already covered. Add four tests that exercise this path:

- connect_timeout_new_exact         exact-size buffer
- connect_timeout_new_oversize_clamped  oversize buffer, clamped
- connect_timeout_new_undersize     undersize -> -EINVAL, optlen
                                    untouched
- connect_timeout_old_exact         exact-size buffer for OLD optname

Suggested-by: Stanislav Fomichev <sdf@fomichev.me>
Suggested-by: Bobby Eshleman <bobbyeshleman@meta.com>
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260507-getsock_two-v2-5-5873111d9c12@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Add a single kselftest covering the proto_ops getsockopt_iter
conversions for AF_NETLINK and AF_VSOCK, using one fixture per protocol:

netlink:

NETLINK_PKTINFO covers the flag-style int path (exact size, oversize
clamp, undersize -EINVAL); NETLINK_LIST_MEMBERSHIPS covers the
size-discovery path that always reports the required buffer length back
via optlen, even when the user buffer is too small to receive any group
bits.

vsock:
SO_VM_SOCKETS_BUFFER_SIZE covers the u64 path (exact size, oversize
clamp, undersize -EINVAL).

Each fixture also exercises an unknown optname and a bogus level so
the returned-length / errno semantics preserved by the sockopt_t
conversion are pinned down.

Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20260501-getsock_one-v1-3-810ce23ea70e@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>