[NETFILTER]: nf_conntrack_h323: fix compile error with CONFIG_IPV6=m, CONFIG_NF_CONNTRACK_H323=y

Fix this by letting NF_CONNTRACK_H323 depend on (IPV6 || IPV6=n).

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: David S. Miller <davem@davemloft.net>