core: only attempt to deserialize state from LUO on boot

Avoid trying to query for our LUO session on reexec/softreboot/reload/etc.
Currently /dev/liveupdate is only accessible to root so it's not a big
issue, but this might change in the future, so make sure nobody can
play games with us.

Follow-up for 257c35c1a3

src/core/manager.c

@@ -2194,8 +2194,10 @@ int manager_startup(Manager *m, FILE *serialization, FDSet *fds, Hashmap *named_
                         m->soft_reboots_count++;
 
                 /* If a LUO (Live Update Orchestrator) session from a previous kexec is available, restore
-                 * preserved file descriptors into the appropriate service fd stores now, before coldplug. */
-                (void) manager_luo_restore_fd_stores(m);
+                 * preserved file descriptors into the appropriate service fd stores now, before coldplug.
+                 * Only do this when booting up (i.e., skip on reexec/soft reboot/etc.) */
+                if (m->previous_objective < 0)
+                        (void) manager_luo_restore_fd_stores(m);
 
                 /* Pick up fds passed via the LISTEN_FDS=/LISTEN_FDNAMES= protocol that are tagged with a
                  * unit id ("unit-id|fdname"), and route them into the matching unit's fd store. Untagged