usnic: ensure all messages are sent on the data channel

Messages should go on the data channel, even if they're short.  Only
ACKs go on the priority channel.

opal/mca/btl/usnic/btl_usnic_module.c

@@ -12,7 +12,7 @@
  *                         All rights reserved.
  * Copyright (c) 2006      Sandia National Laboratories. All rights
  *                         reserved.
- * Copyright (c) 2009-2015 Cisco Systems, Inc.  All rights reserved.
+ * Copyright (c) 2009-2016 Cisco Systems, Inc.  All rights reserved.
  * Copyright (c) 2014      Los Alamos National Security, LLC. All rights
  *                         reserved.
  * Copyright (c) 2014      Intel, Inc. All rights reserved
@@ -1205,7 +1205,7 @@ usnic_send(
         /* assign length */
         sseg->ss_len = sizeof(opal_btl_usnic_btl_header_t) + frag->sf_size;
 
-        sseg->ss_channel = USNIC_PRIORITY_CHANNEL;
+        sseg->ss_channel = USNIC_DATA_CHANNEL;
         sseg->ss_base.us_btl_header->tag = tag;
 #if MSGDEBUG1
         opal_output(0, "INLINE send, sseg=%p", (void *)sseg);

opal/mca/btl/usnic/btl_usnic_send.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2015 Cisco Systems, Inc.  All rights reserved.
+ * Copyright (c) 2013-2016 Cisco Systems, Inc.  All rights reserved.
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -76,6 +76,8 @@ opal_btl_usnic_post_segment(
                 sseg->ss_len);
 #endif
 
+    assert(channel_id == USNIC_DATA_CHANNEL);
+
     /* Send the segment */
     ret = fi_send(channel->ep,
             sseg->ss_ptr,
@@ -126,6 +128,8 @@ opal_btl_usnic_post_ack(
                 sseg->ss_len);
 #endif
 
+    assert(channel_id == USNIC_PRIORITY_CHANNEL);
+
     ret = fi_send(channel->ep,
             sseg->ss_ptr,
             sseg->ss_len + mca_btl_usnic_component.prefix_send_offset,