DNS queries are not sent to upstream DNS server

[scareything]

#774 correctly added a check to DNS queries to ensure that recursion was requested before sending to the upstream DNS server, however there is problem with how the DNS flags are assigned, and this prevents queries from being sent to the upstream server when it is set.

The DNS flags are being set by overlapping a bit field with the uint16 value from the message, but this isn't portable. Instead we need to retrieve the individual flags out of the message with masking.