btl/tcp: output the IP address correctly

Per
#3035 (comment),
it looks like the IP address for a given interface is being stashed in
two places: on the endpoint and on the module.

1. On the endpoint, it is storing the moral equivalent of a
   (struct sockaddr_in.sin_addr).
2. On the module, it is storing a full (struct sockaddr_storage).

The call to opal_net_get_hostname() expects a full (struct sockaddr*)
-- not just the stripped-down (struct sockaddr_in.sin_addr).  Hence,
when the original code was passing in the endpoint's (struct
sockaddr_in.sin_addr) and opal_net_get_hostname() was treating it
like a (struct sockaddr), hilarity ensued (i.e., we got the wrong
output).

This commit eliminates the call to opal_net_get_hostname() and just
calls inet_ntop() directly to convert the (struct
sockaddr_in.sin_addr) to a string.

NOTE: Per the github comment cited above, there can be a disparity
between the IP address cached on the endpoint vs. the IP address
cached on the module.  This only happens with interfaces that have
more than one IP address.  This commit does not fix that issue.

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

Author: jsquyres

opal/mca/btl/tcp/btl_tcp_proc.c

@@ -901,17 +901,22 @@ void mca_btl_tcp_proc_accept(mca_btl_tcp_proc_t* btl_proc, struct sockaddr* addr
     /* No further use of this socket. Close it */
     CLOSE_THE_SOCKET(sd);
     {
-        char *addr_str = NULL, *tmp, *pnet;
+        char *addr_str = NULL, *tmp;
+        char ip[128];
+        ip[sizeof(ip) - 1] = '\0';
+
         for (size_t i = 0; i < btl_proc->proc_endpoint_count; i++) {
             mca_btl_base_endpoint_t* btl_endpoint = btl_proc->proc_endpoints[i];
             if (btl_endpoint->endpoint_addr->addr_family != addr->sa_family) {
                 continue;
             }
-            pnet = opal_net_get_hostname((struct sockaddr*)&btl_endpoint->endpoint_addr->addr_inet);
+            inet_ntop(btl_endpoint->endpoint_addr->addr_family,
+                      (void*) &(btl_endpoint->endpoint_addr->addr_inet),
+                      ip, sizeof(ip) - 1);
             if (NULL == addr_str) {
-                (void)asprintf(&tmp, "\n\t%s", pnet);
+                (void)asprintf(&tmp, "\n\t%s", ip);
             } else {
-                (void)asprintf(&tmp, "%s\n\t%s", addr_str, pnet);
+                (void)asprintf(&tmp, "%s\n\t%s", addr_str, ip);
                 free(addr_str);
             }
             addr_str = tmp;