extensions: libxt_sctp: Add translation to nft

extensions: libxt_sctp: Add translation to nft

Add translation for sctp to nftables.
Full translation of this match awaits the support for --chunk-types
option.

Examples:

$ sudo iptables-translate -A INPUT -p sctp --dport 80 -j DROP
nft add rule ip filter INPUT sctp dport 80 counter drop

$ sudo iptables-translate -A INPUT -p sctp ! --sport 80:100 -j ACCEPT
nft add rule ip filter INPUT sctp sport != 80-100 counter accept

Signed-off-by: Shivani Bhardwaj <shivanib134@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>