Minor code fixes

Minor code fixes
 [ISC-Bugs #19566] When trying to find the zone for a name for ddns allow
 the name to be at the apex of the zone.
 [ISC-Bugs #19617] Restrict length of interface name read from command line
 in dhcpd - based on a patch from David Cantrell at Red Hat.
 [ISC-Bugs #20039] Correct some error messages in dhcpd.c
 [ISC-Bugs #20070] Better range check on values when creating a DHCID.
 [ISC-Bugs #20198] Avoid writing past the end of the field when adding
 overly long file or server names to a packet and add a log message
 if the configuration supplied overly long names for these fields.
 [ISC-Bugs #21497] Add a little more randomness to rng seed in client