Specify the maximum modulation and coding scheme (MCS) index for
802.11n mandatory rates.
The value 255 indicates that no maximum MCS index
is specified. No maximum MCS index is specified for 802.11n
mandatory rates by default.
Besides 255, the specified maximum MCS index for 802.11n supported
rates must be no less than the specified maximum MCS index for 802.11n
mandatory rates.