When an interface has transferred exbibytes
(> 0.8 EiB, i.e. > 819 PiB) of traffic,
the short display is rounded incorrectly.

For example:
bytes 2154408931384050514 (275.0 PiB)
while correct is (1913.4 PiB)

This happens because we times the rx/tx bytes values by 10,
then calculate the short version from that result:

lib/interface.c:ife_print_long()

tx = ptr->stats.tx_bytes;
short_tx = tx * 10;
if (tx > 1125899906842624ull) {
  short_tx /= 1125899906842624ull;
  Text = "PiB";
}

But multiplying anything more than 819 PiB by 10 overflows a ull
which is a uint64_t (max value of 9223372036854775807).

We'll never get accuracy over 8192 PiB (2^64) when using ull,
but we can at least correctly handle values between 819 - 8192 PiB.