Specifies the drop algorithm running at this queue and
threshold.
'tailDrop' indicates that this queue and threshold drops
packet using tail-drop algorithm. This value is configurable
only if 'tailDrop' bit in the value of qosIfCapabilities object
for the same ifIndex and traffic direction is set.
'wred' indicates that WRED algorithm is used. This value is
configurable only if 'wred' bit in the value of
qosIfCapabilities object for the same ifIndex and traffic
direction is set.