selftests/tc-testing: Fix Error: Specified qdisc kind is unknown.

All TEQL tests assume that sch_teql module is loaded. Load module in tdc.sh
before running qdisc tests.

Fixes following example error when running tests via tdc.sh for all TEQL
tests:

 # $ sudo ./tdc.py -d eth2 -e 84a0
 #  -- ns/SubPlugin.__init__
 # Test 84a0: Create TEQL with default setting
 # exit: 2
 # exit: 0
 # Error: Specified qdisc kind is unknown.
 #
 # -----> teardown stage *** Could not execute: "$TC qdisc del dev $DUMMY handle 1: root"
 #
 # -----> teardown stage *** Error message: "Error: Invalid handle.
 # "
 # returncode 2; expected [0]
 #
 # -----> teardown stage *** Aborting test run.
 #
 # <_io.BufferedReader name=3> *** stdout ***
 #
 # <_io.BufferedReader name=5> *** stderr ***
 # "-----> teardown stage" did not complete successfully
 # Exception <class '__main__.PluginMgrTestFail'> ('teardown', 'Error: Specified qdisc kind is unknown.\n', '"-----> teardown stage" did not complete successfully') (caught in test_runner, running test 2 84a0 Create TEQL with default setting stage teardown)
 # ---------------
 # traceback
 #   File "/images/src/linux/tools/testing/selftests/tc-testing/./tdc.py", line 495, in test_runner
 #     res = run_one_test(pm, args, index, tidx)
 #   File "/images/src/linux/tools/testing/selftests/tc-testing/./tdc.py", line 434, in run_one_test
 #     prepare_env(args, pm, 'teardown', '-----> teardown stage', tidx['teardown'], procout)
 #   File "/images/src/linux/tools/testing/selftests/tc-testing/./tdc.py", line 245, in prepare_env
 #     raise PluginMgrTestFail(
 # ---------------
 # accumulated output for this test:
 # Error: Specified qdisc kind is unknown.
 #
 # ---------------
 #
 # All test results:
 #
 # 1..1
 # ok 1 84a0 - Create TEQL with default setting # skipped - "-----> teardown stage" did not complete successfully

Fixes: cc62fbe1

 ("selftests/tc-testing: add selftests for teql qdisc")
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Reviewed-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>