linux/concepts: fix a mistake on atomics return value

[mtardy]

See more details in the specification¹:

The BPF_FETCH modifier is optional for simple atomic operations, and
always set for the complex atomic operations. If the BPF_FETCH flag is set, then the operation also overwrites src with the value that was in memory before it was modified.

Note that we could be even more explicit like they do with something like: "value that was in memory before it was modified".

Footnotes

1. https://www.kernel.org/doc/html/v6.5/bpf/instruction-set.html#atomic-operations ↩

[dylandreimerink]

Good catch, thanks! 🚀