add relaxed_ordering option (#324)

* add relaxed_ordering option

add an environment variable that allows to control setting the
IBV_ACCESS_RELAXED_ORDERING flag when registering memory with the
ibv_reg_mr* functions.

* missed a spot

[ROCm/rocshmem commit: 2ae2033648]

projects/rocshmem/docs/compile_and_run.rst

@@ -90,3 +90,6 @@ You can control the behavior of rocSHMEM by using the following environment vari
     * - ROCSHMEM_GDA_ALTERNATE_QP_PORTS
       - 1
       - Enables/Disables having QPs alternate their mappings across rocSHMEM contexts. This helps saturate bandwidth on multiport bonded interfaces.
+    * - ROCSHMEM_GDA_PCIE_RELAXED_ORDERING
+      - 0
+      - Enables PCIe Relaxed Ordering when registering the symemtric heap with the RDMA NICs.