ipv6: sctp: implement sctp_v6_destroy_sock()

Dmitry Vyukov reported a memory leak using IPV6 SCTP sockets.

We need to call inet6_destroy_sock() to properly release
inet6 specific fields.
Reported-by: NDmitry Vyukov <dvyukov@google.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sctp/socket.c

@@ -7379,6 +7379,13 @@ struct proto sctp_prot = {
 
 #if IS_ENABLED(CONFIG_IPV6)
 
+#include <net/transp_v6.h>
+static void sctp_v6_destroy_sock(struct sock *sk)
+{
+	sctp_destroy_sock(sk);
+	inet6_destroy_sock(sk);
+}
+
 struct proto sctpv6_prot = {
 	.name		= "SCTPv6",
 	.owner		= THIS_MODULE,
@@ -7388,7 +7395,7 @@ struct proto sctpv6_prot = {
 	.accept		= sctp_accept,
 	.ioctl		= sctp_ioctl,
 	.init		= sctp_init_sock,
-	.destroy	= sctp_destroy_sock,
+	.destroy	= sctp_v6_destroy_sock,
 	.shutdown	= sctp_shutdown,
 	.setsockopt	= sctp_setsockopt,
 	.getsockopt	= sctp_getsockopt,