Specify time-related settings in the Timing Protocol section are in seconds.

[felix.the.red_gmail.com]

Summary

Add a line of text to clarify the Timing Protocol section uses seconds,
and how they are parsed.

From the original PR:
In its Protocol Timing section, The dhclient.conf(5) manpage lists several time-related settings.
The unit in which the delays and timers are expressed is not specified.
Is the unit second, millisecond, minute, or anything else?
This should be part of the documentation.

PR: 261682

Test Plan

Read convert_num() in sbin/dhclient/parse.c.