MINOR: http: export the smp_fetch_cookie function

Remove the static attribute of smp_fetch_cookie, and declare the
function in proto/proto_http.h for future use.
diff --git a/include/proto/proto_http.h b/include/proto/proto_http.h
index 065a0ea..6370e2d 100644
--- a/include/proto/proto_http.h
+++ b/include/proto/proto_http.h
@@ -119,6 +119,8 @@
 struct chunk *http_error_message(struct session *s, int msgnum);
 struct redirect_rule *http_parse_redirect_rule(const char *file, int linenum, struct proxy *curproxy,
                                                const char **args, char **errmsg, int use_fmt);
+int smp_fetch_cookie(struct proxy *px, struct session *l4, void *l7, unsigned int opt,
+                 const struct arg *args, struct sample *smp, const char *kw);
 
 enum http_meth_t find_http_meth(const char *str, const int len);
 
diff --git a/src/proto_http.c b/src/proto_http.c
index 2febda4..24c7cf8 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -10539,10 +10539,10 @@
  * The cookie name is in args and the name length in args->data.str.len.
  * Accepts exactly 1 argument of type string. If the input options indicate
  * that no iterating is desired, then only last value is fetched if any.
- * The returned sample is of type CSTR.
+ * The returned sample is of type CSTR. Can be used to parse cookies in other
+ * files.
  */
-static int
-smp_fetch_cookie(struct proxy *px, struct session *l4, void *l7, unsigned int opt,
+int smp_fetch_cookie(struct proxy *px, struct session *l4, void *l7, unsigned int opt,
                  const struct arg *args, struct sample *smp, const char *kw)
 {
 	struct http_txn *txn = l7;