Add extra-info line that tracks the number of consensus downloads over each pluggable transport
In legacy/trac#5040 (moved), Karsten suggested to add yet another line for measuring obfsbridge stats.
He wants a dirreq-v3-transport line with the exact same format as bridge-ip-transports, that counts consensus fetches instead of direct connections. This will improve the granularity of bridge statistics, and it will help us count users accurately in scenarios like flashproxy (where each client is actually a flashproxy bridge).
This means that we should be considering the GEOIP_CLIENT_NETWORKSTATUS_V2 and GEOIP_CLIENT_NETWORKSTATUS events in this case, instead of GEOIP_CLIENT_CONNECT.