- Don't oversize the buffer fragment. PAGE_SIZE - (curaddr & PAGE_MASK)
may be greater than the total length of the buffer.
- Don't use roundup2(len, alignment) to calculate the buffer fragment
size. The length of current bounced fragment is not subject to alignment
restriction, and next fragment should start at the page boundary.
Tested by: bz, s199p.wa1k9r@gmail.com