don't close connection when getting OFPT_ERROR_MSG

It's a really bad idea to close a connection with a switch when
getting OFPT_ERROR_MSG. For example, ryu should continue to run about
'Request was not understood' type error because ryu doesn't know what
request types the switch supports.

Let applications catch OFPT_ERROR_MSG and do whatever they want. The
core should not do anything.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

ryu/controller/handler.py

@@ -134,7 +134,6 @@ class ErrorMsgHandler(object):
         msg = ev.msg
         LOG.debug('error msg ev %s type 0x%x code 0x%x %s',
                   msg, msg.type, msg.code, str(msg.data))
-        msg.datapath.is_active = False
 
 
 @register_cls(HANDSHAKE_DISPATCHER)