On init, backup the frequency tracking registers (PHYRegister 0x18 and 0x38) so that we can restore them when frequency tracking is finished.

Start Frequency Tracking

1. Enable PHYRegisterLock

2. Write 0xFFEA to PHYRegister 0x18

3. Write 0x689 to PHYRegister 0x38

4. Disable PHYRegisterLock

End Frequency Tracking

1. Enable PHYRegisterLock

2. Restore the backed up value of PHYRegister 0x18

3. Restore the backed up value of PHYRegister 0x38

4. Disabled PHYRegisterLock