server: increase default max pdu length to 1024

It was set low to 64 to debug issues with fragmentation and
defragmentation of packages. Bump version to 3 as well since
this breaks the protocol with older clients.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/server.c b/server.c
index c3502cd..1e1e9d0 100644
--- a/server.c
+++ b/server.c
@@ -102,7 +102,7 @@
 	cmd->pdu_len	= le32_to_cpu(cmd->pdu_len);
 
 	switch (cmd->version) {
-	case FIO_SERVER_VER2:
+	case FIO_SERVER_VER3:
 		break;
 	default:
 		log_err("fio: bad server cmd version %d\n", cmd->version);