ntp: update 4.2.8p6

QA error fix:
ERROR: QA Issue: ntp: Files/directories were installed but not shipped in any package:
  /usr/libexec

CVES addressed:

Bug 2948 / CVE-2015-8158
Bug 2945 / CVE-2015-8138: origin: Zero Origin Timestamp Bypass
Bug 2942 / CVE-2015-7979: Off-path Denial of Service (DoS) attack on authenticated broadcast mode
Bug 2940 / CVE-2015-7978: Stack exhaustion in recursive traversal of restriction list
Bug 2939 / CVE-2015-7977: reslist NULL pointer dereference
Bug 2938 / CVE-2015-7976: ntpq saveconfig command allows dangerous characters in filenames
Bug 2937 / CVE-2015-7975: nextvar() missing length check
Bug 2936 / CVE-2015-7974: Skeleton Key: Missing key check allows impersonation between authenticated peers
Bug 2935 / CVE-2015-7973: Deja Vu: Replay attack on authenticated broadcast mode
Bug 2947 / CVE-2015-8140: ntpq vulnerable to replay attacks
Bug 2946 / CVE-2015-8139: Origin Leak: ntpq and ntpdc, disclose origin

NTP-4.2.8p5
NtpBug2956: Small-step/Big-step CVE-2015-5300

Bug #2829 Clean up pipe_fds in ntpd.c
Bug #2887 stratum -1 config results as showing value 99.
Bug #2932 Update leapsecond file info in miscopt.html.
Bug #2934 tests/ntpd/t-ntp_scanner.c has a magic constant wired in.
Bug #2944 errno is not preserved properly in ntpdate after sendto call.
Bug #2952 peer associations were broken by the fix for NtpBug2901 CVE-2015-7704
Bug #2954 Version 4.2.8p4 crashes on startup on some OSes.
Bug #2957 'unsigned int' vs 'size_t' format clash.
Bug #2958 ntpq: fatal error messages need a final newline.
Bug #2962 truncation of size_t/ptrdiff_t on 64bit targets.
Bug #2965 Local clock didn't work since 4.2.8p4.
Bug #2967 ntpdate command suffers an assertion failure
Bug #2969 Seg fault from ntpq/mrulist when looking at server with lots of clients.
Bug #2971 ntpq bails on ^C: select fails: Interrupted system call

Signed-off-by: Armin Kuster <akuster808@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>