Moderate: ntp security, bug fix, and enhancement update (Oracle Linux 7)

[4.2.6p5-22]
- check origin timestamp before accepting KoD RATE packet (CVE-2015-7704)
- allow only one step larger than panic threshold with -g (CVE-2015-5300)

[4.2.6p5-20]
- validate lengths of values in extension fields (CVE-2014-9297)
- drop packets with spoofed source address ::1 (CVE-2014-9298)
- reject packets without MAC when authentication is enabled (CVE-2015-1798)
- protect symmetric associations with symmetric key against DoS attack (CVE-2015-1799)
- fix generation of MD5 keys with ntp-keygen on big-endian systems (CVE-2015-3405)
- add option to set Differentiated Services Code Point (DSCP) (#1202828)
- add nanosecond support to SHM refclock (#1117702)
- allow creating all SHM segments with owner-only access (#1122012)
- allow different thresholds for forward and backward step (#1193154)
- allow symmetric keys up to 32 bytes again (#1191111)
- don't step clock for leap second with -x option (#1191122)
- don't drop packets with source port below 123 (#1171640)
- retry joining multicast groups (#1207014)
- increase memlock limit again (#1053569)
- warn when monitor can't be disabled due to limited restrict (#1191108)
- use larger RSA exponent in ntp-keygen (#1191116)
- fix crash in ntpq mreadvar command (#1180721)
- move sntp kod database to allow SELinux labeling (#1082934)
- fix typos in ntpd man page (#1195211)
- improve documentation of restrict command (#1213953)