MINOR: http-htx: Export functions to update message authority and host

These functions will be used by HTTP health checks when a request is formatted
before sending it.
diff --git a/include/proto/http_htx.h b/include/proto/http_htx.h
index 617417a..99d56b4 100644
--- a/include/proto/http_htx.h
+++ b/include/proto/http_htx.h
@@ -45,6 +45,9 @@
 int http_replace_header_value(struct htx *htx, struct http_hdr_ctx *ctx, const struct ist data);
 int http_replace_header(struct htx *htx, struct http_hdr_ctx *ctx, const struct ist name, const struct ist value);
 int http_remove_header(struct htx *htx, struct http_hdr_ctx *ctx);
+int http_update_authority(struct htx *htx, struct htx_sl *sl, const struct ist host);
+int http_update_host(struct htx *htx, struct htx_sl *sl, const struct ist uri);
+
 unsigned int http_get_htx_hdr(const struct htx *htx, const struct ist hdr,
 			      int occ, struct http_hdr_ctx *ctx, char **vptr, size_t *vlen);
 unsigned int http_get_htx_fhdr(const struct htx *htx, const struct ist hdr,