[mac] don't append header termination IE2 for empty data payload (#7123)
[mac] don't append header termination IE2 for empty data payload (#7123)

We do not require the HT2 IE if the only thing that follows the header
is the MIC.

This commit reverts #6941.
jwhui/openthread,jwhui/openthread,srickardti/openthread,abtink/openthread,openthread/openthread,openthread/openthread,abtink/openthread,srickardti/openthread,abtink/openthread,jwhui/openthread,srickardti/openthread,openthread/openthread,srickardti/openthread,jwhui/openthread,abtink/openthread,openthread/openthread