import: wire up SYSTEMD_IMPORT_BTRFS_{SUBVOL,QUOTA} to importd

Btrfs quotas are actually being enabled in systemd-importd via
setup_machine_directory(), not in systemd-{import,pull} where those
environment variables are checked. Therefore, also check them in
systemd-importd and avoid enabling quotas if requested by the user.

Fixes: #18421
Fixes: #15903
Fixes: #24387

src/shared/machine-pool.c

@@ -22,7 +22,7 @@ static int check_btrfs(void) {
         return F_TYPE_EQUAL(sfs.f_type, BTRFS_SUPER_MAGIC);
 }
 
-int setup_machine_directory(sd_bus_error *error) {
+int setup_machine_directory(sd_bus_error *error, bool use_btrfs_subvol, bool use_btrfs_quota) {
         int r;
 
         r = check_btrfs();
@@ -31,8 +31,14 @@ int setup_machine_directory(sd_bus_error *error) {
         if (r == 0)
                 return 0;
 
+        if (!use_btrfs_subvol)
+                return 0;
+
         (void) btrfs_subvol_make_label("/var/lib/machines");
 
+        if (!use_btrfs_quota)
+                return 0;
+
         r = btrfs_quota_enable("/var/lib/machines", true);
         if (r < 0)
                 log_warning_errno(r, "Failed to enable quota for /var/lib/machines, ignoring: %m");