sandbox: vm: reduce vm_page order field size to 4 bits

sandbox/vm/page.c

@@ -28,9 +28,15 @@ static size_t page_order_bytes[] = {
 	[VM_PAGE_32M]  = 0x2000000,
 	[VM_PAGE_64M]  = 0x4000000,
 	[VM_PAGE_128M] = 0x8000000,
+#if 0
+	/* vm can support pages of this size, but
+	   vm_page_t only has 4 bits with which to store
+	   the page order, which cannot accomodate these
+	   larger order numbers */
 	[VM_PAGE_256M] = 0x10000000,
 	[VM_PAGE_512M] = 0x20000000,
 	[VM_PAGE_1G]   = 0x40000000,
+#endif
 };
 
 void vm_page_init_array()