SMPP transport attempts to send MT messages before protocol is ready.

```
2014-01-27 17:09:57+0000 [VumiRedis,client] Unhandled Error
        Traceback (most recent call last):
          File "/mnt/praekelt/vumi-go/ve/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 382, in callback
            self._startRunCallbacks(result)
          File "/mnt/praekelt/vumi-go/ve/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 490, in _startRunCallbacks
            self._runCallbacks()
          File "/mnt/praekelt/vumi-go/ve/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 577, in _runCallbacks
            current.result = callback(current.result, *args, **kw)
          File "/mnt/praekelt/vumi-go/ve/src/vumi/vumi/transports/base.py", line 176, in _process_message
            d = maybeDeferred(self.handle_outbound_message, message)
        --- <exception caught here> ---
          File "/mnt/praekelt/vumi-go/ve/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 139, in maybeDeferred
            result = f(*args, **kw)
          File "/mnt/praekelt/vumi-go/ve/src/vumi/vumi/transports/smpp/smpp_transport.py", line 149, in handle_outbound_message
            message, self.service.get_protocol())
          File "/mnt/praekelt/vumi-go/ve/src/vumi/vumi/transports/smpp/processors.py", line 343, in handle_outbound_message
            return protocol.submit_sm_long(
        exceptions.AttributeError: 'NoneType' object has no attribute 'submit_sm_long'

```