Log header drop.

Author: Lukasa

hyper/http20/connection.py

@@ -282,6 +282,7 @@ def putheader(self, header, argument, stream_id=None):
         # the call to `_get_stream` to ensure that we don't accidentally hide
         # bugs just because the user sent a connection header.
         if header.lower() == 'connection':
+            log.debug('Ignoring connection header with value %s', argument)
             return
 
         stream.add_header(header, argument)