selftests/landlock: Add tests for FS topology changes with network rules

Add 2 tests to the layout1 fixture:
* topology_changes_with_net_only: Checks that FS topology
  changes are not denied by network-only restrictions.
* topology_changes_with_net_and_fs: Make sure that FS topology
  changes are still denied with FS and network restrictions.

This specifically test commit d7220364 ("landlock: Allow FS topology
changes for domains without such rule type").

Cc: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Link: https://lore.kernel.org/r/20231027154615.815134-1-mic@digikod.net


Signed-off-by: Mickaël Salaün <mic@digikod.net>