[NETFILTER]: nf_conntrack: fix NF_CT_TUPLE_DUMP for IPv4

NF_CT_TUPLE_DUMP prints IPv4 addresses as IPv6, fix this and use printk
(guarded by #ifdef DEBUG) directly instead of pr_debug since the tuple
is usually printed at the end of line and we don't want to include a
log-level.

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