kist: use tcpi_notsent_bytes where possible
In my rough measurements on a busy relay, Tor's main thread spends about 2% of its time calling ioctl. If tcpi_notsent_bytes is available, we can avoid calling ioctl and make tor about 2% faster.
In my rough measurements on a busy relay, Tor's main thread spends about 2% of its time calling ioctl. If tcpi_notsent_bytes is available, we can avoid calling ioctl and make tor about 2% faster.