doc: fix formatting in testpmd guide

doc: fix formatting in testpmd guide

Minor formatting error related to code block noticed when reading the doc.
Fix it and some other errors.

Fixes: c7217b9dd8ef ("app/testpmd: change log level at run time")
Fixes: 3c272b280a50 ("app/testpmd: add commands for RSS queue region")
Fixes: e38ea44f1714 ("app/testpmd: add configuration for input set")
Fixes: 08e0b3440baf ("app/testpmd: add option to configure UDP tunnel port")
Fixes: e977e4199a8d ("app/testpmd: add commands to load/unload BPF filters")
Cc: stable@dpdk.org
Signed-off-by: Kevin Traynor <ktraynor@redhat.com>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>