lib/s3_req: increase the multi-part done request buffer size
lib/s3_req: increase the multi-part done request buffer size

For uploads with many parts, the static 2K buffer can be easily
exhausted.

Signed-off-by: David Disseldorp <589a549dc9f982d9f46aeeb82a09ab6d87ccf1d8@suse.de>

ddiss/elasto,ddiss/elasto