Refer to sessions by ID instead of memory address

Using the unique ID for the session is easier to use than an address. This
also allows the removal of all pointer values from the maxadmin output
which is never useful to the end user.

server/core/dcb.c

@@ -2063,7 +2063,12 @@ dprintDCB(DCB *pdcb, DCB *dcb)
         dcb_printf(pdcb, "\tProtocol:                   %s\n",
                    dcb->protoname);
     }
-    dcb_printf(pdcb, "\tOwning Session:     %p\n", dcb->session);
+
+    if (dcb->session && dcb->session->state != SESSION_STATE_DUMMY)
+    {
+        dcb_printf(pdcb, "\tOwning Session:     %lu\n", dcb->session->ses_id);
+    }
+
     if (dcb->writeq)
     {
         dcb_printf(pdcb, "\tQueued write data:  %d\n", gwbuf_length(dcb->writeq));