CONFIG_NF_NAT_PROTO_DCCP is no more a tristate. When set to y, NAT
support for DCCP protocol is built-in into nf_nat.ko.

footprint test:

(nf_nat_proto_)           | dccp   || nf_nat
--------------------------+--------++--------
no builtin                | 409800 || 2241312
DCCP builtin              |   -    || 2578968
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>