Originally, only a host name was used to associate a
DHCPv6 request with a specific IPv6 address.  Further testing
demonstrates that this is an unreliable method and, instead,
a client-id or DUID needs to be used.  According to DHCPv6
standards, this id can be a duid-LLT, duid-LL, or duid-UUID
even though dnsmasq will accept almost any text string.

Although validity checking of a specified string makes sure it is
hexadecimal notation with bytes separated by colons, there is no
rigorous check to make sure it meets the standard.

Documentation and schemas have been updated.
Signed-off-by: NGene Czarcinski <gene@czarc.net>
Signed-off-by: NLaine Stump <laine@laine.org>