Throughout the code we use rate_n_flags & 0xff to extract the lower byte
of the rate_n_flags u32 that contains the information about the rate.
Add a #define and remove the use of the magic number.
Signed-off-by: NDaniel Halperin <dhalperi@cs.washington.edu>
Signed-off-by: NWey-Yi Guy <wey-yi.w.guy@intel.com>