net.c: Use dynamically allocated buffer for non-sendfile uploading
net.c: Use dynamically allocated buffer for non-sendfile uploading

And use a larger buffer size. This avoids allocating unused memory when
using sendfile-based uploads, and allows for a larger buffer for
non-sendfile uploads.

Tilka/ncdc,srijan/ncdc,Tilka/ncdc,srijan/ncdc,srijan/ncdc