ntp: upgrade 4.2.8p3 -> 4.2.8p4

4.2.8p4 fixed following 13 low- and medium-severity vulnerabilities:

  * Bug 2941 CVE-2015-7871
  * Bug 2922 CVE-2015-7855
  * Bug 2921 CVE-2015-7854
  * Bug 2920 CVE-2015-7853
  * Bug 2919 CVE-2015-7852
  * Bug 2918 CVE-2015-7851
  * Bug 2917 CVE-2015-7850
  * Bug 2916 CVE-2015-7849
  * Bug 2913 CVE-2015-7848
  * Bug 2909 CVE-2015-7701
  * Bug 2902 CVE-2015-7703
  * Bug 2901 CVE-2015-7704, CVE-2015-7705
  * Bug 2899 CVE-2015-7691, CVE-2015-7692, CVE-2015-7702

And three bugs: Bug 2382, 1774, 1593

Details at:
  http://support.ntp.org/bin/view/Main/SecurityNotice#Recent_Vulnerabilities



Signed-off-by: Wenzong Fan <wenzong.fan@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>