This attribute indicates the sum of delay metrics of trunks that make
up the selected route returned by RouteSelector. The delay metric of
a trunk is equal to half the measuredRoundTripDelay operational
attribute of the trunk. If the delay metrics at both ends of a trunk
differ, the larger metric is used for that trunk. If a route could not be
selected for whatever reason then the routeDelayMetric is set to a
value 999999 intended to symbolize unknown delay. For manual
routes the value of routeDelayMetric is also 999999. This is
because RouteSelector does not verify manual routes, thus
routeDelayMetric is unknown.