BUG-890: Update ietf-inet-types and ietf-yang-types with RFC6991

Change-Id: Ie6f6891835f761c440650a2d0d7990db20f9d52f
Signed-off-by: Robert Varga <rovarga@cisco.com>
(cherry picked from commit 1569ca177ce5a40abf69d44766e346d72c01db4d)