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.h

@@ -5,4 +5,4 @@
 
 #include "sd-bus.h"
 
-int setup_machine_directory(sd_bus_error *error);
+int setup_machine_directory(sd_bus_error *error, bool use_btrfs_subvol, bool use_btrfs_quota);