selftests/ipc: skip msgque test when MSG_COPY is unsupported

selftests/ipc: skip msgque test when MSG_COPY is unsupported

msgque kselftest uses msgrcv(..., MSG_COPY) to copy messages.  When the
kernel is built without CONFIG_CHECKPOINT_RESTORE, prepare_copy() is
stubbed out and msgrcv() returns -ENOSYS.  The test currently reports this
as a failure even though it is simply a missing feature/configuration.

Skip the test when msgrcv() fails with ENOSYS.

Link: https://lkml.kernel.org/r/20260210135359.178636-1-jouyeol8739@gmail.com
Signed-off-by: UYeol Jo <jouyeol8739@gmail.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>