chattr-util: generalize chattr manipulation for files with secrets from journalctl

This moves the code for setting chattr file attributes appropriate for
"secrets" files from journalctl into generic chattr-util.c code so that
we can use it elsewhere.

Also, let's reuse the "bitwise" logic already implemented in the chattr
code, instead of doing it again.

src/tmpfiles/tmpfiles.c

@@ -1355,7 +1355,7 @@ static int fd_set_attribute(Item *item, int fd, const char *path, const struct s
                 return log_error_errno(procfs_fd, "Failed to re-open '%s': %m", path);
 
         unsigned previous, current;
-        r = chattr_full(NULL, procfs_fd, f, item->attribute_mask, &previous, &current, true);
+        r = chattr_full(NULL, procfs_fd, f, item->attribute_mask, &previous, &current, CHATTR_FALLBACK_BITWISE);
         if (r == -ENOANO)
                 log_warning("Cannot set file attributes for '%s', maybe due to incompatibility in specified attributes, "
                             "previous=0x%08x, current=0x%08x, expected=0x%08x, ignoring.",