netfilter: conntrack: remove UDP-Lite conntrack support

netfilter: conntrack: remove UDP-Lite conntrack support

UDP-Lite (RFC 3828) socket support was recently retired from the core
networking stack. As a follow-up of that, drop the connection tracker
and NAT support for UDP-Lite in Netfilter.

This patch removes CONFIG_NF_CT_PROTO_UDPLITE and scrubs UDP-Lite
awareness from the conntrack core, NAT core, nft_ct, and ctnetlink.
Please note that stateless packet inspection, matching, ipsets or
logging support for IPPROTO_UDPLITE is preserved.

As conntrack no longer extracts UDP-Lite ports or tracks its L4 state,
when performing NAT the UDP-Lite checksum cannot be updated anymore.
That is an expected and acceptable consequence of removing UDP-Lite
conntrack module.

Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Florian Westphal <fw@strlen.de>