netfilter: nft_ct: Remove confirmation check for NFT_CT_ID

Since commit 656c8e9c ("netfilter: conntrack: Use consistent ct id
hash calculation") the ct id will not change from initialization to
confirmation.  Removing the confirmation check allows for things like
adding an element to a 'typeof ct id' set in prerouting upon reception
of the first packet of a new connection, and then being able to
reference that set consistently both before and after the connection
is confirmed.

Fixes: 656c8e9c

 ("netfilter: conntrack: Use consistent ct id hash calculation")
Signed-off-by: Brett Mastbergen <brett.mastbergen@gmail.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>