ntp security update

[4.2.6p5-12.0.1.el6_9.1]

• add disable monitor to default ntp.conf [CVE-2013-5211]
  [4.2.6p5-12.el6_9.1]
• fix buffer overflow in datum refclock driver (CVE-2017-6462)
• fix crash with invalid unpeer command (CVE-2017-6463)
• fix potential crash with invalid server command (CVE-2017-6464)
  [4.2.6p5-12]
• don’t limit rate of packets from sources (CVE-2016-7426)
• don’t change interface from received packets (CVE-2016-7429)
• fix calculation of root distance again (CVE-2016-7433)
• require authentication for trap commands (CVE-2016-9310)
• fix crash when reporting peer event to trappers (CVE-2016-9311)
  [4.2.6p5-11]
• don’t allow spoofed packets to demobilize associations (CVE-2015-7979,
  CVE-2016-1547)
• don’t allow spoofed packet to enable symmetric interleaved mode
  (CVE-2016-1548)
• check mode of new source in config command (CVE-2016-2518)
• make MAC check resilient against timing attack (CVE-2016-1550)