serial: don't set O_NDELAY, as it is more or less O_NONBLOCK

Applications like osmocon will set O_NONBLOCK themselves or have it done
indirectly by registering it with libosmocore/select.c code.
diff --git a/src/serial.c b/src/serial.c
index 11ba503..a025ae9 100644
--- a/src/serial.c
+++ b/src/serial.c
@@ -63,7 +63,7 @@
 	struct termios tio;
 
 	/* Open device */
-	fd = open(dev, O_RDWR | O_NOCTTY | O_NDELAY);
+	fd = open(dev, O_RDWR | O_NOCTTY);
 	if (fd < 0) {
 		dbg_perror("open");
 		return -errno;