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): #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 #1770 there are other use cases that requires larger omit time period.