This attribute indicates the urgency with which packets on the
LCh's path are emitted by this trunk. The emissionPriority
translates into the trunk's emission queue. Zero (0) indicates the
highest emissionPriority, while three (3) indicates the lowest.
Packets with a higher emissionPriority (or numerically less) are put
on an emission queue which is serviced before a queue which
accepts packets of a lower emissionPriority and hence experience
smaller delays traversing congested trunks.