BUILD: http-rules: include proxy.h from http_rules.c

Many proxy functions are called there but the include was missing and
inherited via cfgparse.h.

src/http_rules.c

@@ -28,6 +28,7 @@
 #include <haproxy/http_rules.h>
 #include <haproxy/log.h>
 #include <haproxy/pool.h>
+#include <haproxy/proxy.h>
 #include <haproxy/sample.h>
 #include <haproxy/tools.h>
 #include <haproxy/version.h>