extensions: libxt_conntrack: use bitops for state negation

extensions: libxt_conntrack: use bitops for state negation

Currently, state_xlate_print function prints statemask as comma-separated sequence of enabled
statemask flags. But if we have inverted conntrack ctstate condition then we have to use more
complex expression because nft not supports syntax like "ct state != related,established".

Reproducer:
$ iptables -A INPUT -d 127.0.0.1/32 -p tcp -m conntrack ! --ctstate RELATED,ESTABLISHED -j DROP
$ nft list ruleset
...
meta l4proto tcp ip daddr 127.0.0.1 ct state != related,established counter packets 0 bytes 0 drop
...

it will fail if we try to load this rule:
$ nft -f nft_test
../nft_test:6:97-97: Error: syntax error, unexpected comma, expecting newline or semicolon

Cc: Florian Westphal <fw@strlen.de>
Signed-off-by: Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>
Signed-off-by: Florian Westphal <fw@strlen.de>