correct size based on alignment

This commit was SVN r5322.

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

@@ -39,7 +39,7 @@ mca_ptl_tcp_module_t mca_ptl_tcp_module = {
     {
     &mca_ptl_tcp_component.super,
     16, /* max size of request cache */
-    sizeof(mca_ptl_tcp_send_frag_t), /* bytes required by ptl for a request */
+    sizeof(mca_ptl_tcp_send_request_t) - sizeof(mca_pml_base_send_request_t), /* bytes required by ptl for a request */
     0, /* max size of first fragment */
     0, /* min fragment size */
     0, /* max fragment size */