use vlong to defend against wraparound.  identify mystery integer as µs.

Reference: /n/sources/patch/applied/dhcpdone
Date: Wed Apr  2 22:05:47 CES 2008
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/ip/dhcpd/dhcpd.c	Wed Apr  2 22:03:30 2008
+++ /sys/src/cmd/ip/dhcpd/dhcpd.c	Wed Apr  2 22:03:19 2008
@@ -64,7 +64,7 @@
 int	minlease = MinLease;
 int	staticlease = StaticLease;
 
-ulong	start;
+uvlong	start;
 
 static int v6opts;
 
@@ -199,10 +199,10 @@
 void
 timestamp(char *tag)
 {
-	ulong t;
+	uvlong t;
 
 	t = nsec()/1000;
-	syslog(0, blog, "%s %lud", tag, t - start);
+	syslog(0, blog, "%s %lludµs", tag, t - start);
 }
 
 void
@@ -401,7 +401,7 @@
 		dhcp(rp);
 	else
 		bootp(rp);
-timestamp("done");
+	timestamp("done");
 }
 
 static void