Add rcu locking around call to rt6_check_expired in
ip6_negative_advice.
Fixes: ec7b3e64852f ("net/ipv6: Make from in rt6_info rcu protected") Reported-by: syzbot+2422c9e35796659d2273@syzkaller.appspotmail.com Signed-off-by: David Ahern <dsahern@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>