Set a small chuck size for the protostream

Otherwise we default to a 8MB chunck size which is what we allocate for
each protostream and we end up in cases where we only use 70 bytes out
of the 8MBs.

Test: n/a
Bug: 282153574
Change-Id: I3aeeb27c389edffd118bffdd0a3e12d72fa42a6d