Revert "netfilter: ipv6: nf_defrag: drop skb dst before queueing"

This reverts commit ad8b1ffc.

From Florian Westphal <fw@strlen.de>:

	It causes kernel crash for locally generated ipv6 fragments
	when netfilter ipv6 defragmentation is used.

	The faulty commit is not essential for -stable, it only
	delays netns teardown for longer than needed when that netns
	still has ipv6 frags queued.  Much better than crash :-/

Signed-off-by: Sasha Levin <sashal@kernel.org>