doc: fix formatting in testpmd guide

[ upstream commit ea2066b ]

Fix formatting in testpmd user guide for hairpin operation.

Fixes: 01817b1 ("app/testpmd: change hairpin queues setup")

Signed-off-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Acked-by: Xiaoyun Li <xiaoyun.li@intel.com>
Reviewed-by: Bing Zhao <bingz@nvidia.com>

doc/guides/testpmd_app_ug/run_app.rst

@@ -524,8 +524,10 @@ The command line options are:
 
 *   ``--hairpin-mode=0xXX``
 
-    Set the hairpin port mode with bitmask, only valid when hairpin queues number is set.
-    bit 4 - explicit Tx flow rule
-    bit 1 - two hairpin ports paired
-    bit 0 - two hairpin ports loop
+    Set the hairpin port mode with bitmask, only valid when hairpin queues number is set::
+
+	bit 4 - explicit Tx flow rule
+	bit 1 - two hairpin ports paired
+	bit 0 - two hairpin ports loop
+
     The default value is 0. Hairpin will use single port mode and implicit Tx flow mode.