Set unicast_sock uc_ttl to -1 so that we select the right ttl,
instead of sending packets with a 0 ttl.
Bug added in commit 
be9f4a44e7d4 (ipv4: tcp: remove per net tcp_sock)
Signed-off-by: Hiroaki SHIMODA <shimoda.hiroaki@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
                .sk_allocation  = GFP_ATOMIC,
                .sk_flags       = (1UL << SOCK_USE_WRITE_QUEUE),
        },
-       .pmtudisc = IP_PMTUDISC_WANT,
+       .pmtudisc       = IP_PMTUDISC_WANT,
+       .uc_ttl         = -1,
 };
 
 void ip_send_unicast_reply(struct net *net, struct sk_buff *skb, __be32 daddr,