ntp: import ntp-4.2.8p16

Security: NtpBUg3767, NtpBug3808, NtpBug3807 (CVE-2023-26555)
MFC after: immediately

MFV r344878:

4.2.8p12 --> 4.2.8p13

MFC after: immediately
Security: CVE-2019-8936
VuXML: c2576e14-36e2-11e9-9eda-206a8a720317
Obtained from: nwtime.org