src/utils_latency.c: Store "bin_width" as cdtime_t.

src/utils_latency.c: Store "bin_width" as cdtime_t.

This solves the integer overflow when passing huge latency values to
latency_counter_add(). In addition to fixing the overflow the function
will now ignore values that are larger than LLONG_MAX, i.e. the longest
possible latency is 272 years. As a nice side-effect, the precission of
latency_counter_get_percentile() is improved.

Issue: #1131