BUG/MEDIUM: pattern: Pattern node has type of "struct pat_idx_elt" in place of "struct eb_node"

The free() function must free the "struct pat_idx_elt".

This bug was introduced by commit ed66c29 (REORG: acl/pattern: extract
pattern matching from the acl file and create pattern.c), no backport
is needed.
diff --git a/src/pattern.c b/src/pattern.c
index 4f049f7..aef2a00 100644
--- a/src/pattern.c
+++ b/src/pattern.c
@@ -769,11 +769,14 @@
 void free_pattern_tree(struct eb_root *root)
 {
 	struct eb_node *node, *next;
+	struct pat_idx_elt *elt;
+
 	node = eb_first(root);
 	while (node) {
 		next = eb_next(node);
 		eb_delete(node);
-		free(node);
+		elt = container_of(node, struct pat_idx_elt, node);
+		free(elt);
 		node = next;
 	}
 }