[libvirt] Proposed: replace radvd with dnsmasq for Router Advertizing

[Gene Czarcinski]

I have been doing some testing and dnsmasq is capable of handling the 
service currently provided by radvd.  To implement this in dnsmasq 
requires the following:

if an IPv6 dhcp-range is specified, then add:
       enable-ra

if no IPv6 dhcp-range is specified, then add:
       dhsp-range=<IPv6-subnet>,ra-only

Tested.  The second one will work with basic dnsmasq-2.6.3.  The first 
one and dhcp-range itself only works with dnsmasq-2.64 (when released) 
or dnsmasq-2.63+patches.

Since dnsmasq-2.48 does not support IPv6 dhcp but does handle IPv6 for 
dns and CentOS 6 does include radvd, I also propose that a libvirtd.conf 
option be added.  If the option is not present or set off, then radvd is 
used.  If the option is set on, then dnsmasq is used.

At some point in the future, it can be decided whether to keep using 
radvd or not.

Comments?  Suggestions?

Gene