vm: Add missing modules to the 'expression->derivation-in-linux-vm' initrd.

Fixes a regression introduced in
bc499b113a, whereby the default initrd
used by 'expression->derivation-in-linux-vm' would lack all the usual
modules: virtio, nls_iso8859-1, etc.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Pass
 #:linux-modules to 'base-initrd'.

gnu/system/vm.scm

@@ -143,6 +143,7 @@ made available under the /xchg CIFS share."
                          (return initrd)
                          (base-initrd %linux-vm-file-systems
                                       #:linux linux
+                                      #:linux-modules %base-initrd-modules
                                       #:virtio? #t
                                       #:qemu-networking? #t))))