[PATCH v4 20/20] net/txgbe: fix to enable Tx desc check

[Zaiyu Wang]

> Minor AI stuff here:
Thank you for the review. Based on the feedback, I have made the following adjustments:
> ## WARNINGS
> 
> ### 1. Bit manipulation should use RTE_BIT32() macro
Fixed.

> ### 2. Conditional compilation without corresponding documentation update
No code change
This patch does not change the intended behavior of Tx desc check. Due to hardware
limitation, IPsec and desc check cannot be enabled at the same time; the original design
was to enable desc check by default when IPsec is not in use. The previous code had a bug
that prevented this from working correctly, and this patch simply fixes that. Therefore a
separate document update is not needed.
> 
> ## INFO
> 
> ### 1. Potential logic optimization
No code change
I chose not to extract the bitmask into a separate variable to keep the change minimal and
the code concise.
> 
> ### 2. Parentheses around `using_ipsec` unnecessary
Fixed.