PYTHON-2453 Correctly add ServerApi to all w=0 writes

Author: ShaneHarvey

pymongo/bulk.py

@@ -296,7 +296,6 @@ def _execute_command(self, generator, write_concern, session,
                 run.op_type, self.collection.codec_options)
 
             while run.idx_offset < len(run.ops):
-                sock_info.add_server_api(cmd, session)
                 if session:
                     # Start a new retryable write unless one was already
                     # started for this command.

pymongo/message.py

@@ -893,6 +893,7 @@ def __init__(self, database_name, command, sock_info, operation_id,
         self.compress = True if sock_info.compression_context else False
         self.op_type = op_type
         self.codec = codec
+        sock_info.add_server_api(command, session)
 
     def _batch_command(self, docs):
         namespace = self.db_name + '.$cmd'