orangefs: keep the readdir entry size 64-bit in fill_from_part()

In the Linux kernel, the following vulnerability has been resolved: orangefs: keep the readdir entry size 64-bit in fill_from_part() fill_from_part() computes the size of a directory entry in size_t but stores it in a __u32. An entry length near U32_MAX wraps it to a small value, bypasses the bounds check, and is then used to index the entry, reading far past the directory part -- an out-of-bounds read that oopses the kernel. Compute the size as a u64 so it cannot truncate; the bounds check then rejects the entry. The trailer is supplied by the userspace client.