MB-11016 Deal with byte order of UPR mutation flag

Make sure upr-producer send 'flags' in the mutation in network
byte-order by not converting the value which is already in network
byte-order when stored.

Change-Id: Idbadb5deb427af2e456e57c0001ab7cb1c33fcd2
Reviewed-on: http://review.couchbase.org/37413
Tested-by: David Liao <david.liao@couchbase.com>
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>