tcp: Remove use of inet6_sk and add IPv6 checks to tracepoint

386fd5d ("tcp: Check daddr_cache before use in tracepoint") was the
second version of the tracepoint fixup patch. This patch is the delta
between v2 and v3.  Specifically, remove the use of inet6_sk and check
sk_family as requested by Eric and add IS_ENABLED(CONFIG_IPV6) around
the use of sk_v6_rcv_saddr and sk_v6_daddr as done in sock_common (noted
by Cong).

Signed-off-by: David Ahern <dsahern@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Tested-by: Song Liu <songliubraving@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/trace/events/tcp.h

@@ -43,13 +43,15 @@ TRACE_EVENT(tcp_retransmit_skb,
 		p32 = (__be32 *) __entry->daddr;
 		*p32 =  inet->inet_daddr;
 
-		/* IPv6 socket ? */
-		if (inet6_sk(sk)) {
+#if IS_ENABLED(CONFIG_IPV6)
+		if (sk->sk_family == AF_INET6) {
 			pin6 = (struct in6_addr *)__entry->saddr_v6;
 			*pin6 = sk->sk_v6_rcv_saddr;
 			pin6 = (struct in6_addr *)__entry->daddr_v6;
 			*pin6 = sk->sk_v6_daddr;
-		} else {
+		} else
+#endif
+		{
 			pin6 = (struct in6_addr *)__entry->saddr_v6;
 			ipv6_addr_set_v4mapped(inet->inet_saddr, pin6);
 			pin6 = (struct in6_addr *)__entry->daddr_v6;