services: udev: Explicitly depend on (gnu build linux-boot).

* gnu/services/base.scm (udev-shepherd-service): Wrap 'start' method in
'with-imported-modules'.

gnu/services/base.scm

@@ -1996,7 +1996,10 @@ (define udev-shepherd-service
          (requirement '(root-file-system))
 
          (documentation "Populate the /dev directory, dynamically.")
-         (start #~(lambda ()
+         (start
+          (with-imported-modules (source-module-closure
+                                  '((gnu build linux-boot)))
+            #~(lambda ()
                 (define udevd
                   ;; 'udevd' from eudev.
                   #$(file-append udev "/sbin/udevd"))
@@ -2053,7 +2056,7 @@ (define (wait-for-udevd)
                   ;; Wait for things to settle down.
                   (system* #$(file-append udev "/bin/udevadm")
                            "settle")
-                      pid)))
+                  pid))))
          (stop #~(make-kill-destructor))
 
          ;; When halting the system, 'udev' is actually killed by
@@ -2061,7 +2064,7 @@ (define (wait-for-udevd)
          ;; Thus, make sure it is not respawned.
          (respawn? #f)
          ;; We need additional modules.
-         (modules `((gnu build linux-boot)
+         (modules `((gnu build linux-boot)        ;'make-static-device-nodes'
                     ,@%default-modules))
 
          (actions (list (shepherd-action