CLEANUP: http_ana: Make use of the return value of stream_generate_unique_id()
Even if `unique_id` and `s->unique_id` are identical it is a bit odd to
`isttest()` `unique_id` and then use `s->unique_id` in the call to `http_add_header()`.
This "issue" was introduced in a17e66289c08a5bfadc1bb5b5f2c618c9299fe1b,
because before that commit the function returned the length of the ID, as it
was not an ist.
diff --git a/src/stream.c b/src/stream.c
index 29d1a60..d18031e 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -2850,7 +2850,7 @@
/* Generates a unique ID based on the given <format>, stores it in the given <strm> and
* returns the unique ID.
-
+ *
* If this function fails to allocate memory IST_NULL is returned.
*
* If an ID is already stored within the stream nothing happens existing unique ID is