When large(1) is the setting all large frames are permissable
out that port. fragment_if_possible(2) is used when the outport
wants ip frames fragmented before transmission. All other non
fragmentable large frames will be transmitted large. small(3)
requires that no large frames be transmitted out this interface.
If a frame can be fragmented then it can be transmitted out the
interface. auto(4) is a special setting that will allow a device
to negotiate which of the other three settings to use as the
operational mode.
The default of this object is product specific.