No limit to omit time period

[davidBar-On]

• Version of iperf3 (or development branch, such as master or
  3.1-STABLE) to which this pull request applies:
  master

• Issues fixed (if any): iperf3 -O (--omit) to get more than 60 seconds omit time #1770

• Brief description of code changes (suitable for use as a commit message):
  Change the --omit time period limit from 60 to the same limit as --time (86,400 seconds = one day).
  My assumption is that the 60 seconds was just to be more user friendly, assuming that the omit period is only to omit possible performance fluctuations at the first few seconds of the tests. Per iperf3 -O (--omit) to get more than 60 seconds omit time #1770 there are other use cases that requires larger omit time period.

[bmah888]

Thanks for the PR! Some of these hard limits exist to put sane boundaries on some of the test parameters, the idea being that if a user really needed to do say very long tests they should be at least knowlegable enough to modify the code and recompile it.

In this case, there (probably?) isn't any particular resource constraint caused by having longer --omit times, so it probably makes sense to change the bound as in this PR.