[NETFILTER]: nf_conntrack: fix NF_CONNTRACK_PROC_COMPAT dependency

NF_CONNTRACK_PROC_COMPAT depends on NF_CONNTRACK_IPV4, not NF_CONNTRACK.

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