In panic() print current timestamp, which matches timestamp in the dump

header.  This will help to correlate console server logs with dump files,
no matter how precise is clock on a console server appliance, and how
buggy the appliance is.

sys/kern/kern_shutdown.c

@@ -764,7 +764,7 @@ vpanic(const char *fmt, va_list ap)
 #ifdef SMP
 	printf("cpuid = %d\n", PCPU_GET(cpuid));
 #endif
-
+	printf("time = %ld\n", time_second);
 #ifdef KDB
 	if (newpanic && trace_on_panic)
 		kdb_backtrace();