Specify the modulation and coding scheme (MCS) index for 802.11n
multicast rates.
The value 4294967295 indicates that no MCS index is specified.
No MCS index is specified for 802.11n multicast rates by default.
Besides 4294967295, the specified MCS index for 802.11n multicast
rates must be no less than the specified maximum MCS index for 802.11n
mandatory rates.
Before configure the MCS index for 802.11n multicast rates, the maximum
MCS index for 802.11n mandatory rates must be configured