inet: prefer sizeof with parenthesis

[juanarbol]

This is not precisely a strict rule, but this syntax is reinforced in many large C projects like the Linux kernel and cURL.

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From my POV, using parenthesis when using sizeof() is just less ambiguous.

But feel free to reject if u don't find this useful.

[saghul]

I think overall we have more usage of no parentheses across the project, can you check?

[bnoordhuis]

sizeof(x) is about 6.3x more prevalent than sizeof x

[saghul]

Then it's settled!