Add the test for additional reference to chains that are explicitly created
by RTM_NEWCHAIN message.
The test result:
1..1
ok 1 c2b4 - soft lockup alarm will be not generated after delete the prio 0
filter of the chain
commit c9a82bec02c3 ("net/sched: cls_api: Fix lockup on flushing explicitly
created chain")
Signed-off-by: Mingshuai Ren <renmingshuai@xxxxxxxxxx>