netfilter: Kconfig: default DCCP/SCTP conntrack support to the protocol config values

When conntrack and DCCP/SCTP protocols are enabled, chances are good
that people also want DCCP/SCTP conntrack and NAT support.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>