[test] update `Cert_9_2_17_Orphan` to make it more robust (#7581)
[test] update `Cert_9_2_17_Orphan` to make it more robust (#7581)

This commit updates `Cert_9_2_17_Orphan` packet verification to check
that the two leaders are sending MLE advertisement before checking
for child attach (Child ID response). The current test checked this
after the child attach but leader 1 is turned off 5 seconds after
the child is attached which may not be enough time to ensure rx
of an advertisement (which every 30 seconds on average).
jwhui/openthread,abtink/openthread,abtink/openthread,abtink/openthread,openthread/openthread,srickardti/openthread,openthread/openthread,srickardti/openthread,srickardti/openthread,jwhui/openthread,srickardti/openthread,abtink/openthread,openthread/openthread,jwhui/openthread,openthread/openthread,jwhui/openthread