libxt_sctp: fix array out of range in print_chunk

libxt_sctp: fix array out of range in print_chunk

For chunk type ASCONF, ASCONF_ACK and FORWARD_TSN, sctp_chunk_names[].chunk_type
is not equal to the corresponding index in sctp_chunk_names[]. Using this field
leads to a segmentation fault (index out of range).

Example
$ iptables -A INPUT -p sctp --chunk-type all ASCONF,ASCONF_ACK,FORWARD_TSN -j ACCEPT
$ iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
Segmentation fault

Signed-off-by: huaibin Wang <huaibin.wang@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>