BUG/MINOR: srv-state: fix incorrect output of state file

Eric Webster reported that the state file wouldn't reload in 1.6.5
while it used to work in 1.6.4. The issue is that headers are now
missing from the output when a specific backend is dumped since
commit 4c1544d ("BUG/MEDIUM: stats: show servers state may show an
empty or incomplete result"). This patch fixes this by introducing
a dump state.

It must be backported to 1.6.

src/dumpstats.c

@@ -3200,15 +3200,22 @@ static int stats_dump_servers_state_to_buffer(struct stream_interface *si)
 
 	chunk_reset(&trash);
 
-	if (!appctx->ctx.server_state.px) {
+	if (appctx->st2 == STAT_ST_INIT) {
+		if (!appctx->ctx.server_state.px)
+			appctx->ctx.server_state.px = proxy;
+		appctx->st2 = STAT_ST_HEAD;
+	}
+
+	if (appctx->st2 == STAT_ST_HEAD) {
 		chunk_printf(&trash, "%d\n# %s\n", SRV_STATE_FILE_VERSION, SRV_STATE_FILE_FIELD_NAMES);
 		if (bi_putchk(si_ic(si), &trash) == -1) {
 			si_applet_cant_put(si);
 			return 0;
 		}
-		appctx->ctx.server_state.px = proxy;
+		appctx->st2 = STAT_ST_INFO;
 	}
 
+	/* STAT_ST_INFO */
 	for (; appctx->ctx.server_state.px != NULL; appctx->ctx.server_state.px = curproxy->next) {
 		curproxy = appctx->ctx.server_state.px;
 		/* servers are only in backends */