Data with ms time ignored without error

[farshidtz]

Submitting senml data with milliseconds timestamp (instead of seconds) is accepted by the server (202 status code), but nothing is stored.

 curl -i --location --request POST 'http://localhost:8085/data/' \
--header 'Content-Type: application/json' \
--data-raw '[{"n":"test","t":1593441174505,"v":2}]'
HTTP/1.1 202 Accepted
Content-Type: application/json;version=master

It should be rejected with 400 error.

Moreover, content-type is set to application/json for empty body.