maple_tree: add testing for restoring maple state to active

maple_tree: add testing for restoring maple state to active

Restoring maple status to ma_active on overflow/underflow when mas->node
was NULL could have happened in the past, but was masked by a bug in
mas_walk().  Add test cases that triggered the bug when the node was
mas->node prior to fixing the maple state setup.

Add a few extra tests around restoring the active maple status.

Link: https://lore.kernel.org/all/202506191556.6bfc7b93-lkp@intel.com/
Link: https://lkml.kernel.org/r/20250624154823.52221-2-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>