ipv6: don't get lwtstate twice in ip6_rt_copy_init()

Commit 80f1a0f4 ("net/ipv6: Put lwtstate when destroying fib6_info")
partially fixed the kmemleak [1], lwtstate can be copied from fib6_info,
with ip6_rt_copy_init(), and it should be done only once there.

rt->dst.lwtstate is set by ip6_rt_init_dst(), at the start of the function
ip6_rt_copy_init(), so there is no need to get it again at the end.

With this patch, lwtstate also isn't copied from RTF_REJECT routes.

[1]:
unreferenced object 0xffff880b6aaa14e0 (size 64):
  comm "ip", pid 10577, jiffies 4295149341 (age 1273.903s)
  hex dump (first 32 bytes):
    01 00 04 00 04 00 00 00 10 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<0000000018664623>] lwtunnel_build_state+0x1bc/0x420
    [<00000000b73aa29a>] ip6_route_info_create+0x9f7/0x1fd0
    [<00000000ee2c5d1f>] ip6_route_add+0x14/0x70
    [<000000008537b55c>] inet6_rtm_newroute+0xd9/0xe0
    [<000000002acc50f5>] rtnetlink_rcv_msg+0x66f/0x8e0
    [<000000008d9cd381>] netlink_rcv_skb+0x268/0x3b0
    [<000000004c893c76>] netlink_unicast+0x417/0x5a0
    [<00000000f2ab1afb>] netlink_sendmsg+0x70b/0xc30
    [<00000000890ff0aa>] sock_sendmsg+0xb1/0xf0
    [<00000000a2e7b66f>] ___sys_sendmsg+0x659/0x950
    [<000000001e7426c8>] __sys_sendmsg+0xde/0x170
    [<00000000fe411443>] do_syscall_64+0x9f/0x4a0
    [<000000001be7b28b>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
    [<000000006d21f353>] 0xffffffffffffffff

Fixes: 6edb3c96 ("net/ipv6: Defer initialization of dst to data path")
Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -996,7 +996,6 @@ static void ip6_rt_copy_init(struct rt6_info *rt, struct fib6_info *ort)
 	rt->rt6i_src = ort->fib6_src;
 #endif
 	rt->rt6i_prefsrc = ort->fib6_prefsrc;
-	rt->dst.lwtstate = lwtstate_get(ort->fib6_nh.nh_lwtstate);
 }
 
 static struct fib6_node* fib6_backtrack(struct fib6_node *fn,