Update the stack to use the new CoAP return code 2.04/2.05 values.

Update the stack to use the new CoAP return code 2.04/2.05 values.

Since draft-ietf-core-observe-02 (September 16, 2011),
the result value "2.00" was depricated and replaced with "2.05"
for GET a method and "2.04" for POST and PUT methods.

Change-Id: I8061089469609d5ad801fa0456fda326cbc1fc33
Signed-off-by: Stephane Lejeune <stlejeun@cisco.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/2396
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Hauke Mehrtens <hauke.mehrtens@lantiq.com>
Reviewed-by: Patrick Lankswert <patrick.lankswert@intel.com>