selftests: tc: add 'ct' action kconfig dep

When looking for something else in LKFT reports [1], I noticed most of
the tests were skipped because the "teardown stage" did not complete
successfully.

Pedro found out this is due to the fact CONFIG_NF_FLOW_TABLE is required
but not listed in the 'config' file. Adding it to the list fixes the
issues on LKFT side. CONFIG_NET_ACT_CT is now set to 'm' in the final
kconfig.

Fixes: c34b961a ("net/sched: act_ct: Create nf flow table per zone")
Cc: stable@vger.kernel.org
Link: https://qa-reports.linaro.org/lkft/linux-next-master/build/next-20230711/testrun/18267241/suite/kselftest-tc-testing/test/tc-testing_tdc_sh/log [1]
Link: https://lore.kernel.org/netdev/0e061d4a-9a23-9f58-3b35-d8919de332d7@tessares.net/T/ [2]
Suggested-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Tested-by: Zhengchao Shao <shaozhengchao@huawei.com>
Link: https://lore.kernel.org/r/20230713-tc-selftests-lkft-v1-2-1eb4fd3a96e7@tessares.netAcked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/tc-testing/config

@@ -5,6 +5,7 @@ CONFIG_NF_CONNTRACK=m
 CONFIG_NF_CONNTRACK_MARK=y
 CONFIG_NF_CONNTRACK_ZONES=y
 CONFIG_NF_CONNTRACK_LABELS=y
+CONFIG_NF_FLOW_TABLE=m
 CONFIG_NF_NAT=m
 CONFIG_NETFILTER_XT_TARGET_LOG=m