[toranj] update `test-018-child-supervision` to make it more robust (#7687)
[toranj] update `test-018-child-supervision` to make it more robust (#7687)

This commit adds a small wait time between steps in the toranj
`test-018-child-supervision` to help make the test more robust. The
test adds some extra time for child to finish the "child update
request/response" exchange with the parent before enabling MAC
filter.
abtink/openthread,openthread/openthread,srickardti/openthread,abtink/openthread,openthread/openthread,jwhui/openthread,srickardti/openthread,abtink/openthread,srickardti/openthread,abtink/openthread,srickardti/openthread,openthread/openthread,jwhui/openthread,jwhui/openthread,jwhui/openthread,openthread/openthread