tc-testing: add missing 'nsPlugin' to basic.json

since tdc tests for cls_basic need $DEV1, use 'nsPlugin' so that the
following command can be run without errors:

 [root@f31 tc-testing]# ./tdc.py -c basic

Fixes: 4717b053 ("tc-testing: Introduced tdc tests for basic filter")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>