Make find_opt_by_keyword() take a const smartlist

Part of #25988

Signed-off-by: David Goulet <dgoulet@torproject.org>

src/or/parsecommon.c

@@ -426,7 +426,7 @@ find_by_keyword_(smartlist_t *s, directory_keyword keyword,
  * NULL if no such keyword is found.
  */
 directory_token_t *
-find_opt_by_keyword(smartlist_t *s, directory_keyword keyword)
+find_opt_by_keyword(const smartlist_t *s, directory_keyword keyword)
 {
   SMARTLIST_FOREACH(s, directory_token_t *, t, if (t->tp == keyword) return t);
   return NULL;

src/or/parsecommon.h

@@ -314,7 +314,7 @@ directory_token_t *find_by_keyword_(smartlist_t *s,
 #define find_by_keyword(s, keyword) \
   find_by_keyword_((s), (keyword), #keyword)
 
-directory_token_t *find_opt_by_keyword(smartlist_t *s,
+directory_token_t *find_opt_by_keyword(const smartlist_t *s,
                                        directory_keyword keyword);
 smartlist_t * find_all_by_keyword(const smartlist_t *s, directory_keyword k);