io: Handle really long lines

While commit 18b0b45b (io: Handle long lines, Thu Jan 7 17:25:23 2021
+0100) did attempt to address this issue, the buffer really is still to
small when dealing with big-big dependency lists.

Lets make it sufficiently large for now, until the new APKINDEX format
can support multi-line dependencies, making this not needed any more.

[TT: Originally the buffer size was conservative to run on resource
constrained embedded platforms. But since the available memory on those
has also increased much, the adjustment to 128kB makes sense also to
increase performance a little bit. Removing also the iolimit test.]

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>