server6: Fix listening on multicast addresses

Joining a multicast group with an address that can't be received on a
socket is ineffective, at least on linux.
This updates the logic of NewServer in a mostly backwards-compatible
way, to enable listening on arbitrary multicast addresses:

 * Unicast addresses see no user-visible change, but don't join a
   multicast group for which they don't receive traffic anyway
 * Multicast addresses start actually receiving traffic for the group
   they represent, and don't join the default group. **this is a
   behaviour change**: previously they would receive traffic for the
   default group if it was on the same port and **not** for the group
   they represent. I consider that previous behaviour a bug
 * Wildcard addresses, if on the proper port, will join both
   AllDHCPRelayAgentsAndServers and AllDHCPServers **this is a behaviour
   change**: previously only AllDHCPRelayAgentsAndServers was joined
 * Wildcard addresses on another port: no visible change, same as
   unicast case

Signed-off-by: Anatole Denis <natolumin@unverle.fr>

0 files changed, 0 insertions, 0 deletions