selftests/landlock: Test UNIX sockets with any address formats

selftests/landlock: Test UNIX sockets with any address formats

Expand abstract UNIX socket restriction tests by examining different
scenarios for UNIX sockets with pathname or unnamed address formats
connection with scoped domain.

The various_address_sockets tests ensure that UNIX sockets bound to a
filesystem pathname and unnamed sockets created by socketpair can still
connect to a socket outside of their scoped domain, meaning that even if
the domain is scoped with LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET, the
socket can connect to a socket outside the scoped domain.

Signed-off-by: Tahera Fahimi <fahimitahera@gmail.com>
Link: https://lore.kernel.org/r/a9e8016aaa5846252623b158c8f1ce0d666944f4.1725494372.git.fahimitahera@gmail.com
[mic: Remove useless clang-format tags, fix unlink/rmdir calls, drop
capabilities, rename variables, remove useless mknod/unlink calls, clean
up fixture, test write/read on sockets, test sendto() on datagram
sockets, close sockets as soon as possible]
Co-developed-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Mickaël Salaün <mic@digikod.net>