Indicates the current maximum size, in octets, of the MPDU
that may be delivered to the PHY. An MSDU is broken down into
fragments if its size exceeds the value of this attribute
after adding MAC headers and trailers. An MSDU or MMPDU is
fragmented when the resulting frame has an individual address
in the Address1 field, and the length of the frame is larger
than this threshold. The default value for this attribute is
the lesser of 2346 or the aMPDUMaxLength of the attached PHY
and will never exceed the lesser of 2346 or the aMPDUMaxLength
of the attached PHY. The value of this attribute will never
be less than 256.