Fix compilation for userland:

- Use CTASSERT() only in the kernel.
- the root pointer is required by struct vm_object which is accessible
  (maybe incorrectly?) by userland.

sys/vm/vm_radix.h

@@ -44,20 +44,11 @@
 #define	VM_RADIX_HEIGHT	0xf	/* Bits of height in root */
 #define	VM_RADIX_STACK	8	/* Nodes to store on stack. */
 
-CTASSERT(VM_RADIX_HEIGHT >= VM_RADIX_LIMIT);
-
 /* Calculates maximum value for a tree of height h. */
 #define	VM_RADIX_MAX(h)							\
 	    ((h) == VM_RADIX_LIMIT ? ((vm_pindex_t)-1) :		\
 	    (((vm_pindex_t)1 << ((h) * VM_RADIX_WIDTH)) - 1))
 
-#ifdef _KERNEL
-
-struct vm_radix_node {
-	void		*rn_child[VM_RADIX_COUNT];	/* child nodes. */
-    	uint16_t	rn_count;			/* Valid children. */
-};
-
 /*
  * Radix tree root.  The height and pointer are set together to permit
  * coherent lookups while the root is modified.
@@ -66,6 +57,14 @@ struct vm_radix {
 	uintptr_t	rt_root;		/* root + height */
 };
 
+#ifdef _KERNEL
+CTASSERT(VM_RADIX_HEIGHT >= VM_RADIX_LIMIT);
+
+struct vm_radix_node {
+	void		*rn_child[VM_RADIX_COUNT];	/* child nodes. */
+    	uint16_t	rn_count;			/* Valid children. */
+};
+
 void	vm_radix_init(void);
 
 /*