selftests: openat2: Skip testcases that fail with EOPNOTSUPP

[ Upstream commit ac9e0a25 ]

Skip testcases that fail since the requested valid flags combination is not
supported by the underlying filesystem.

Cc: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>