Align all read operations to packet boundaries.
Align all read operations to packet boundaries.

Packets have a fixed size of 0x80 bytes, while a single page is only
0x20 bytes long. Thus each read operation always returns 4 pages at
once. Now, if the end-of-profile pointer is not nicely aligned on a
packet boundary, then the download algorithm won't arrive exactly at the
start address of the ringbuffer, because the ringbuffer is properly
aligned. The consequence is that we won't even notice we reached the
ringbuffer boundary and happily continue reading outside the ringbuffer.
Oops!

This is fixed by aligning the end-of-profile pointer, which guarantees
that all read operations are now nicely aligned to packet boundaries.

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