damos_new_filter() was having a bug that not initializing ->list field of
the returning damos_filter struct, which results in access to
uninitialized memory.  Add a unit test for the function.

Link: https://lkml.kernel.org/r/20230729203733.38949-3-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>