[NETNS][DCCPV4]: Enable DCCPv4 in net namespaces.

This enables sockets creation with IPPROTO_DCCP and enables
the ip level to pass DCCP packets to the DCCP level.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>