osc/rdma: bump the default max dynamic attachments to 64

This commit increaes the osc_rdma_max_attach variable from 32
to 64. The new default is kept low due to the small number
of registration resources on some systems (Cray Aries). A
larger max attachement value can be set by the user on other
systems.

Signed-off-by: Nathan Hjelm <hjelmn@google.com>

ompi/mca/osc/rdma/osc_rdma_component.c

@@ -219,7 +219,7 @@ static int ompi_osc_rdma_component_register (void)
                                             MCA_BASE_VAR_SCOPE_LOCAL, &mca_osc_rdma_component.buffer_size);
     free(description_str);
 
-    mca_osc_rdma_component.max_attach = 32;
+    mca_osc_rdma_component.max_attach = 64;
     opal_asprintf(&description_str, "Maximum number of buffers that can be attached to a dynamic window. "
              "Keep in mind that each attached buffer will use a potentially limited "
              "resource (default: %d)", mca_osc_rdma_component.max_attach);