This attribute specifies the priority that a path holds once it is
established. Zero is the highest priority and four is the lowest. A
path's holdingPriority determines its likelihood of being bumped by
a new path to acquire its bandwidth. The setupPriority, a
complementary attribute, indicates the priority of a path at
establishment time. A new path can bump an existing path if the
new path's setupPriority is higher (numerically less) than the
existing path's holdingPriority.