init pml callback function pointers to null

This commit was SVN r2960.

src/mca/ptl/tcp/src/ptl_tcp.c

@@ -41,7 +41,10 @@ mca_ptl_tcp_module_t mca_ptl_tcp_module = {
     NULL,
     mca_ptl_tcp_matched,
     mca_ptl_tcp_request_init,
-    mca_ptl_tcp_request_fini
+    mca_ptl_tcp_request_fini,
+    NULL,
+    NULL,
+    NULL
     }
 };