Revert "ipv6: grab rt->rt6i_ref before allocating pcpu rt"

This reverts commit 9704f814 which was
upstream commit a94b9367.

Shouldn't have been here, sorry about that.

Reported-by: Chris Rankin <rankincj@gmail.com>
Reported-by: Willy Tarreau <w@1wt.eu>
Cc: Ido Schimmel <idosch@idosch.org>
Cc: Ozgur <ozgur@goosey.org>
Cc: Wei Wang <weiwan@google.com>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>