Bangle GPS Power management

This gets an ACK - seems the length byte is 2 bytes !!!

function UBX_CFG_RATE3() {
  writeGPScmd([0x06,0x08,  // class, id 
         0x06, 0,          // length
         0x00, 0x20,       // b0: 8192ms ie 0x2000,  0x00FF (~65sec)
         0x01, 0x00,       // b2: 
         0x01, 0x00]);     // b4: timeref GPS
}