A negative return value from read in the ntpserver loop should not terminate the
server. 
If the timesource is GPS, announce it in the NTP packets sent.

Reference: /n/sources/patch/applied/ftimesync-as-server
Date: Fri Nov  9 13:36:10 CET 2007
Signed-off-by: matthiasb@acm.org

--- /sys/src/cmd/aux/timesync.c	Fri Nov  9 13:33:21 2007
+++ /sys/src/cmd/aux/timesync.c	Fri Nov  9 13:33:15 2007
@@ -1123,6 +1123,7 @@
 		sysfatal("open %s: %r", data);
 	return fd;
 }
+
 static void
 ntpserver(char *servenet)
 {
@@ -1144,6 +1145,9 @@
 		case Utc:
 			Rootid = "UTC";
 			break;
+		case Gps:
+			Rootid = "GPS";
+			break;
 		case Ntp:
 			/* set by the ntp client */
 			break;
@@ -1155,7 +1159,7 @@
 		n = read(fd, buf, sizeof buf);
 		gettime(&recvts, 0, 0);
 		if(n < 0)
-			return;
+			continue;
 		if(n < Udphdrsize + NTPSIZE)
 			continue;