tc-testing: add ETS scheduler to tdc build configuration

add CONFIG_NET_SCH_ETS to 'config', otherwise test suites using this file
to perform a full tdc run will encounter the following warning:

  ok 645 e90e - Add ETS qdisc using bands # skipped - "-----> teardown stage" did not complete successfully

Fixes: 82c664b6 ("selftests: qdiscs: Add test coverage for ETS Qdisc")
Reported-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>