Fix bug with random IO and network connections

It isn't a supported configuration.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/engines/net.c b/engines/net.c
index 2b48b0a..1a403bd 100644
--- a/engines/net.c
+++ b/engines/net.c
@@ -231,6 +231,10 @@
 		log_err("fio: network connections must be read OR write\n");
 		return 1;
 	}
+	if (td_random(td)) {
+		log_err("fio: network IO can't be random\n");
+		return 1;
+	}
 
 	strcpy(buf, td->o.filename);