Disable ntpd stack gap. When ASLR with STACK GAP != 0 ntpd suffers SIGSEGV.

PR: 241421, 241960
Reported by: Vladimir Zakharov <zakharov.vv@gmail.com>,

		dewayne@heuristicsystems.com.au

Reviewed by: kib, imp (previous version), ian (suggestion)
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D22358