rust/detect: fix too_long_first_doc_paragraph clippy warning

rust/detect: fix too_long_first_doc_paragraph clippy warning

warning: first doc comment paragraph is too long
  --> src/detect/iprep.rs:57:1
   |
57 | / /// value matching is done use `DetectUintData` logic.
58 | | /// isset matching is done using special `DetectUintData` value ">= 0"
59 | | /// isnotset matching bypasses `DetectUintData` and is handled directly
60 | | /// in the match function (in C).
   | |_
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#too_long_first_doc_paragraph
   = note: `#[warn(clippy::too_long_first_doc_paragraph)]` on by default
help: add an empty line

(cherry picked from commit dc3c048b49c5c949836367176b81054e2fbd828e)