Partially revert commit 9402f2a

After doing const analysis, I see it actually writes to the path
variable. Instead of strdup, we can use strdupa which allocates
on the stack and does not need a free. This should be faster
than before.

src/library/filter.c

@@ -174,14 +174,15 @@ static void stack_pop_all_reset(stack_t *_stack)
 
 // this funtion gets full path and checks it against filter
 // returns 1 for keeping the file and 0 for dropping it
-int filter_check(const char *path)
+int filter_check(const char *_path)
 {
-	if (path == NULL) {
+	if (_path == NULL) {
 		msg(LOG_ERR, "filter_check: path is NULL, something is wrong!");
 		return 0;
 	}
 
 	filter_t *filter = global_filter;
+	char *path = strdupa(_path);
 	size_t path_len = strlen(path);
 	size_t offset = 0;
 	// Create a stack to store the filters that need to be checked