Add a maximum observer TTL of 24 hours

Add a maximum observer TTL of 24 hours

A server that transmits notifications mostly in non-confirmable
messages MUST send a notification in a confirmable message instead of
a non-confirmable message at least every 24 hours. This prevents a
client that went away or is no longer interested from remaining in the
list of observers indefinitely.

Change-Id: Ie676f9f5f394fa094b4f2d9fd3a72e2d38d21b24
Signed-off-by: hyuna0213.jo <hyuna0213.jo@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/11497
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jaehong Jo <jaehong.jo@samsung.com>
Reviewed-by: Ashok Babu Channa <ashok.channa@samsung.com>