netfilter: nf_dup: add missing dependencies with NF_CONNTRACK

netfilter: nf_dup: add missing dependencies with NF_CONNTRACK

CONFIG_NF_CONNTRACK=m
CONFIG_NF_DUP_IPV4=y

results in:

   net/built-in.o: In function `nf_dup_ipv4':
>> (.text+0xd434f): undefined reference to `nf_conntrack_untracked'

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
(cherry picked from commit d3340b79ec8222d20453b1e7f261b017d1d09dc9)

Orabug: 24694570

Signed-off-by: Ethan Zhao <ethan.zhao@oracle.com>
Reviewed-by: Dhaval Giani <dhaval.giani@oracle.com>