btl/tcp: use show_help to print the dropped-TCP warning

Make the message more friendly / more detailed, and de-duplicate it
(just in case it happens a lot).

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>

opal/mca/btl/tcp/btl_tcp_proc.c

@@ -16,7 +16,7 @@
  *                         and Technology (RIST). All rights reserved.
  * Copyright (c) 2015-2016 Los Alamos National Security, LLC. All rights
  *                         reserved.
- * Copyright (c) 2015 Cisco Systems, Inc.  All rights reserved.
+ * Copyright (c) 2015-2017 Cisco Systems, Inc.  All rights reserved
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -41,6 +41,7 @@
 #include "opal/util/if.h"
 #include "opal/util/net.h"
 #include "opal/util/proc.h"
+#include "opal/util/show_help.h"
 
 #include "btl_tcp.h"
 #include "btl_tcp_proc.h"
@@ -846,11 +847,13 @@ void mca_btl_tcp_proc_accept(mca_btl_tcp_proc_t* btl_proc, struct sockaddr* addr
                 len = 1024 - strlen(addr_str);
             }
         }
-        opal_output(0, "btl: tcp: Incoming connection from %s does not match known addresses for peer %s [hostname=%s addr=%s]. Drop !\n",
-                    opal_net_get_hostname((struct sockaddr*)addr),
-                    OPAL_NAME_PRINT(btl_proc->proc_opal->proc_name),
-                    btl_proc->proc_opal->proc_hostname,
-                    addr_str);
+        opal_show_help("help-mpi-btl-tcp.txt", "dropped inbound connection",
+                       true, opal_process_info.nodename,
+                       getpid(),
+                       btl_proc->proc_opal->proc_hostname,
+                       OPAL_NAME_PRINT(btl_proc->proc_opal->proc_name),
+                       opal_net_get_hostname((struct sockaddr*)addr),
+                       addr_str);
         free(addr_str);
     }
     OPAL_THREAD_UNLOCK(&btl_proc->proc_lock);

opal/mca/btl/tcp/help-mpi-btl-tcp.txt

@@ -1,6 +1,6 @@
 # -*- text -*-
 #
-# Copyright (c) 2009-2016 Cisco Systems, Inc.  All rights reserved.
+# Copyright (c) 2009-2017 Cisco Systems, Inc.  All rights reserved
 # Copyright (c) 2015-2016 The University of Tennessee and The University
 #                         of Tennessee Research Foundation.  All rights
 #                         reserved.
@@ -85,3 +85,18 @@ or other external events.
   Local PID:  %d
   Peer host:  %s
 #
+[dropped inbound connection]
+Open MPI detected an inbound MPI TCP connection request from a peer
+that appears to be part of this MPI job (i.e., it identified itself as
+part of this Open MPI job), but it is from an IP address that is
+unexpected.  This is highly unusual.
+
+The inbound connection has been dropped, and the peer should simply
+try again with a different IP interface (i.e., the job should
+hopefully be able to continue).
+
+  Local host:          %s
+  Local PID:           %d
+  Peer hostname:       %s (%s)
+  Source IP of socket: %s
+  Known IPs of peer:   %s