[PATCH] mbuf: improve mbuf comments

[Morten Brørup]

> > Typo: TX descriptor -> RX descriptor.
> 
> Another Typo: RX -> Rx ;)
> 
> We agreed to prefer Tx/Rx capitalization in devtools/words-case.txt.
> I personnaly think it is more correct, as it is not an acronym.

It is an acronym, and I think RX/TX is generally more common than Rx/Tx.
However, after checking with Claude, I'll respect the decision to use Rx/Tx.
Please fix the spelling while merging.

My degree is in electrical engineering, not computer science, and Claude confirms that RX/TX is more common for electronics, while Rx/Tx is generally preferred for readability.
So I learned something new about spelling today. ;-)

Claude:
Q: What is the origin of the shorthand form Rx and Tx, and which spelling is most commonly used, RX/TX or Rx/Tx?
A:

The shorthand "Rx" and "Tx" have different origins depending on the context:

In Medicine/Pharmacy
Rx comes from Latin and has been used since medieval times. It's derived from the Latin word "recipe" (meaning "take" or "receive"), which was written at the beginning of prescriptions. Over time, the "R" with a crossed tail evolved into the symbol ℞ and then the shorthand "Rx." This is why prescriptions are often called "Rx."

Tx in medical contexts is a modern abbreviation for "treatment" or "therapy," likely created by analogy with Rx.

In Electronics/Telecommunications
Rx stands for "receive" or "receiver" Tx stands for "transmit" or "transmitter"

These abbreviations became standard in radio, telecommunications, and digital communications to label signal pins, circuits, and data lines.

Capitalization Convention
Both RX/TX and Rx/Tx are widely used, but the preference varies by field:

Electronics/Engineering: RX/TX (all caps) is more common, especially on technical diagrams, circuit boards, and data sheets
Medicine: Rx (capital R, lowercase x) is traditional and standard
General writing: Rx/Tx (mixed case) is often used for readability
In technical documentation for electronics, you'll see both styles, but RX/TX tends to be slightly more prevalent in professional contexts. However, both are perfectly acceptable and widely understood.