extensions: libxt_CONNMARK: Support bit-shifting for --restore,set and save-mark

extensions: libxt_CONNMARK: Support bit-shifting for --restore,set and save-mark

This patch adds a new feature to iptables that allow bitshifting for
--restore,set and save-mark operations. This allows existing logic
operators (and, or and xor) and mask to co-operate with new bitshift
operations.

The intention is to provide uses with more fexible uses of skb->mark
and ct->mark. For example, users can save extra bits in skb->mark:
        skb->mark = ct->mark << 8;

Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Jack Ma <jack.ma@alliedtelesis.co.nz>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>