qcacmn: Fix Supported rates max length

Currently the driver checks for the supported rates IE,
and if the length of the IE is greater than 8, the driver
rejects the IE, according to spec.
But some APs supports 12 rates hence are not scanned.

Fix is to have a supported rates IE length check of 12 instead
of 8.

Change-Id: Ib0e25c94e781ccd44b7f08ea3db6109ad8d6ad22
CRs-Fixed: 2360709