Add three tests that examine different scenarios for abstract UNIX
socket:
1) scoped_domains: Base tests of the abstract socket scoping mechanism
for a landlocked process, same as the ptrace test.
2) scoped_vs_unscoped: Generates three processes with different domains
and tests if a process with a non-scoped domain can connect to other
processes.
3) outside_socket: Since the socket's creator credentials are used
for scoping sockets, this test examines the cases where the socket's
credentials are different from the process using it.
Move protocol_variant, service_fixture, and sys_gettid() from net_test.c
to common.h, and factor out code into a new set_unix_address() helper.
Signed-off-by: Tahera Fahimi <fahimitahera@gmail.com>
Link: https://lore.kernel.org/r/9321c3d3bcd9212ceb4b50693e29349f8d625e16.1725494372.git.fahimitahera@gmail.com
[mic: Fix commit message, remove useless clang-format tags, move
drop_caps() calls, move and rename variables, rename variants, use more
EXPECT, improve comments, simplify the outside_socket test]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
