tc-testing: gitignore, ignore local tdc config file

Comment in tdc_config.py recommends putting customizations in
tdc_config_local.py file that wasn't included in gitignore. Add the local
config file to gitignore.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/tc-testing/.gitignore

@@ -3,3 +3,4 @@ __pycache__/
 plugins/
 *.xml
 *.tap
+tdc_config_local.py