sctp_server,client: drop sctp_data_io_event

sctp_data_io_event sends a sctp_sndrcvinfo control message which
is identical in meaning to sctp_rcvinfo. Right now, both are
sent which causes MSG_CTRUNC.

This just happened to work because sctp_rcvinfo is set first
in the kernel:

        /* Check if we allow SCTP_RCVINFO. */
        if (sp->recvrcvinfo)
                sctp_ulpevent_read_rcvinfo(event, msg);
        /* Check if we allow SCTP_SNDRCVINFO. */
        if (sp->subscribe.sctp_data_io_event)
                sctp_ulpevent_read_sndrcvinfo(event, msg);

Change-Id: I80d6a8ad374447b8cdcfbc35329f88680ac1c5f3
diff --git a/aos/network/sctp_lib.cc b/aos/network/sctp_lib.cc
index 0d31924..318c5a7 100644
--- a/aos/network/sctp_lib.cc
+++ b/aos/network/sctp_lib.cc
@@ -225,6 +225,9 @@
     }
   }
 
+  CHECK_NE(inmessage.msg_flags & MSG_CTRUNC, MSG_CTRUNC)
+      << ": Control message truncated.";
+
   CHECK_LE(size, max_size) << ": Message overflowed buffer on stream "
                            << result->header.rcvinfo.rcv_sid << ".";