Fixes the MOD_NANO build failure

ntp_loopfilter.c: In function 'local_clock':
ntp_loopfilter.c:571: error: 'MOD_NANO' undeclared (first use in this function)
ntp_loopfilter.c:571: error: (Each undeclared identifier is reported only once
ntp_loopfilter.c:571: error: for each function it appears in.)
ntp_loopfilter.c: In function 'loop_config':
ntp_loopfilter.c:896: error: 'MOD_NANO' undeclared (first use in this function)

Taken from
http://cvs.fedoraproject.org/viewvc/devel/ntp/ntp-4.2.4p7-nano.patch?revision=1.1&content-type=text/plain&view=co

See the discussion at
https://bugs.launchpad.net/ubuntu/+source/ntp/+bug/412242 for more
details and links. The below fix is not a correct fix, but only a
workaround. The real fix required changes to kernel/libc headers.

Index: ntp-4.2.4p5/include/ntp_syscall.h
===================================================================
--- ntp-4.2.4p5.orig/include/ntp_syscall.h	2010-05-14 17:34:48.000000000 +0200
+++ ntp-4.2.4p5/include/ntp_syscall.h	2010-05-14 17:35:13.000000000 +0200
@@ -14,6 +14,14 @@
 # include <sys/timex.h>
 #endif
 
+#if defined(ADJ_NANO) && !defined(MOD_NANO)
+#define MOD_NANO ADJ_NANO
+#endif
+
+#if defined(ADJ_TAI) && !defined(MOD_TAI)
+#define MOD_TAI ADJ_TAI
+#endif
+
 #ifndef NTP_SYSCALLS_LIBC
 #ifdef NTP_SYSCALLS_STD
 # define ntp_adjtime(t)		syscall(SYS_ntp_adjtime, (t))