netfilter: nf_ct_dccp: add missing role attributes for DCCP

This patch adds missing role attribute to the DCCP type, otherwise
the creation of entries is not of any use.

The attribute added is CTA_PROTOINFO_DCCP_ROLE which contains the
role of the conntrack original tuple.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>