networks: Support stateful DHCPv6 with prefixes longer than /64
networks: Support stateful DHCPv6 with prefixes longer than /64

Include prefix-len, which defaults to 64, in the --dhcp-range
option to dnsmasq.

Signed-off-by: Mikael Magnusson <4e7a311fb75fcba19ee00424657e05322bd36bf2@users.sourceforge.net>

atxwebs/lxd,hallyn/lxd,hallyn/lxd,Skarlso/lxd,hallyn/lxd,atxwebs/lxd,stgraber/lxd,stgraber/lxd,atxwebs/lxd,Skarlso/lxd,stgraber/lxd,lxc/lxd,Skarlso/lxd,lxc/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,hallyn/lxd,stgraber/lxd,atxwebs/lxd,Skarlso/lxd,stgraber/lxd,mjeanson/lxd,lxc/lxd,stgraber/lxd,mjeanson/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,mjeanson/lxd,lxc/lxd