ntpd: replace openntp's clock discipline with ntpd's

It seems to be much more precise. +2.2k:
   text    data     bss     dec     hex filename
   4670       0       0    4670    123e busybox.t2/networking/ntpd.o
   6838       0       0    6838    1ab6 busybox.t3/networking/ntpd.o

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
1 file changed