Zero-out invalid fields when extracting a "match" and transforming it into a "flow".

Zero-out invalid fields when extracting a "match" and transforming it into a "flow".

When the controller wishes to add a flow entry to the switch, it sends a request with a description of matching flows in a "match".  The switch was adding these exactly as described into the flow tables.  However, when packets arrived, all invalid fields (e.g., the TCP/UDP ports in a non-TCP/UDP packet) are set to zero.  If the rule being added by the controller had not set these invalid fields to zero, the packets would never match.  We now zero out these fields when extracing a "match".

-- Reported by Brandon H. --