[PATCH v4 14/20] net/txgbe: fix link stability for Amber-Lite backplane mode

[Zaiyu Wang]

> Lots of AI feedback here:
> 
> 
> # Review of DPDK Patch: net/txgbe: fix link stability for 40G NIC
> 
> ## Summary
> This patch re-adds direct PHY configuration flow to the txgbe driver to fix unstable link behavior on
> 40G NICs. The previous firmware-based configuration approach was causing link stability issues.
> 
> ## ERRORS
> 
> ### 1. Use-after-free risk in `txgbe_setup_phy_link_aml40`
Fixed.

> ### 2. Missing error propagation in `txgbe_e56_rx_rd_second_code_40g`
Fixed. This function has been changed to void type, as its configuration flow does not produce any error return value under normal operation.

> ### 3. Missing bounds check before array access
Fixed by introducing the RXS_READ_COUNT macro to keep the array size, loop bound, and median calculation always consistent.

> ### 4. Timeout return without cleanup in `txgbe_e56_rxs_calib_adapt_seq_40G`
Not a error.

 
> ## WARNINGS
> 
> ### 1. Hardcoded timeout in multiple locations
Added a comment at the definition of PHYINIT_TIMEOUT clarifying that it is a loop iteration limit, not a fixed time unit. The actual timeout duration depends on the usec_delay() or msleep() value used inside the polling loop. 

> ### 2. Potentially unreachable code after loop
Moved the comment before '}'.

> ### 4. Variable `bypass_ctle` hardcoded but declared as variable
Fixed.

> ### 5. Missing validation of speed parameter in initialization functions
Fixed.


 
> ## INFORMATIONAL
> 
> ### 1. Large function complexity
> ### 2. Magic numbers without symbolic constants
> ### 3. Duplicated initialization sequences The 40G initialization in `txgbe_e56_cfg_40g` 
I prefer not to split the hardware configuration flow at this stage. The current structure closely follows the hardware vendor's recommended initialization sequence.
Most magic numbers are directly from the hardware specification, we do not change them at this stage.
The hardware register requirements for different speeds are not fully identical. Merging them would risk subtle bugs.

> ### 4. Temperature check frequency
This was indeed an omission after moving PHY configuration from firmware to the driver. Previously, temperature tracking was handled by firmware together with hardware setup. We have now added a new patch that implements periodic temperature tracking in the driver. The tracking sequence is invoked every 100ms as recommended. This patch will be submitted in the new version of this patchset.