landlock: Refactor network access mask management

Replace get_raw_handled_net_accesses() and get_current_net_domain() with
a call to landlock_get_applicable_domain().

Cc: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Cc: Mikhail Ivanov <ivanov.mikhail1@huawei-partners.com>
Reviewed-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20241109110856.222842-3-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>