- mcast_group: configure the multicast address, now IPv6
is supported too

- mcast_port: configure the multicast port

- mcast_ttl: configure the multicast TTL/HOP_LIMIT
Signed-off-by: NJulian Anastasov <ja@ssi.bg>
Signed-off-by: NSimon Horman <horms@verge.net.au>