This allows the user to set the priority of a
switch when stacking is enabled on it.
hpStackSwitchPreferredPriority needs to be set
along with hpStackSwitchAdminStatus being set to
'true (1)'.
Note that this is to be used only when enabling
stacking. To set the priority of a switch on
which stacking is already enabled,
use hpStackMemberTable.
hpStackSwitchPreferredPriority is unused when
hpStackSwitchAdminStatus is false (2).