tree-wide: fput[cs]() → fput[cs]_unlocked() wherever that makes sense (#6396)

As a follow-up for db3f45e2d2 let's do the
same for all other cases where we create a FILE* with local scope and
know that no other threads hence can have access to it.

For most cases this shouldn't change much really, but this should speed
dbus introspection and calender time formatting up a bit.

src/machine/machine.c

@@ -199,16 +199,16 @@ int machine_save(Machine *m) {
         if (m->n_netif > 0) {
                 unsigned i;
 
-                fputs("NETIF=", f);
+                fputs_unlocked("NETIF=", f);
 
                 for (i = 0; i < m->n_netif; i++) {
                         if (i != 0)
-                                fputc(' ', f);
+                                fputc_unlocked(' ', f);
 
                         fprintf(f, "%i", m->netif[i]);
                 }
 
-                fputc('\n', f);
+                fputc_unlocked('\n', f);
         }
 
         r = fflush_and_check(f);