There are two issues here:
There are two issues here:

1. newtmgr tool always includes an extraneous rc:0 key-value pair in its
   outgoing datetime commands.
2. Server-side, the firmware parses the "rc" value and writes the result
   to null.

This commit addresses the first issue: Remove the rc entry from the
datetime request.

apache/incubator-mynewt-newt,apache/incubator-mynewt-newt