u16 N PHY Read LPF BW Ctl (u16 offset)

1. Set lut_offset to 0
2. If offset is 0
   1. If this is a 40 MHz channel
      1. Set lut_offset to 0x159
   2. Otherwise
      1. Set lut_offset to 0x154
3. Otherwise
   1. Set lut_offset to offset
4. Read N PHY Table with ID 7, length 1, offset lut_offset, width 16, and dat value

5. Return value & 7