ntp: fix build for no-MMU

ntp: fix build for no-MMU

Code rearrange in the latest ntp version exposed code that used to be
hidden behind HAVE_WORKING_FORK. Put this code back where it belongs.

Fixes:
http://autobuild.buildroot.net/results/9f4/9f4710b451df1a60f95ab6503cfb7788ad998a65/
http://autobuild.buildroot.net/results/d0b/d0b20a6c0f37a8b06841afc2764c8aab6ffd27d2/
http://autobuild.buildroot.net/results/85c/85c89f5e9d36915567b8d14b9c99e3720c866577/

Cc: Artem Panfilov <apanfilov@spectracom.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>