hping3 --fast is 100pps and -u10000 or 10pps and -u100000, currently in contradiction

[`usage.c:24`](https://github.com/antirez/hping/blob/master/usage.c#L24) says the`--fast alias for -i u10000 (10 packets for second)\n"`; however
[`parseoptions.c:505`](https://github.com/antirez/hping/blob/master/parseoptions.c#L505) says `usec_delay.it_interval.tv_usec = 100000;`

If I understood correctly, these numbers assume packet submission time is negligible; hence the `usage.c` or `parseoptions.c` disagree - both should be 10 packets for second (and `-u100000`) or 100 packets for second (and `-u10000`).

Thanks for `hping`!