Envoy should register invalid HTTP as an attempt to send a request

*Title*: Envoy should register invalid HTTP as an attempt to send a request

*Description*:
If a malformed HTTP1 request is sent (e.g. No headers, just "a\r\n\r\n") the HTTP1.1 code will reject it (https://github.com/envoyproxy/envoy/blob/master/source/common/http/http1/codec_impl.cc#L497) and send a 400 without creating a ConnectionManagerImpl::ActiveStream. This means that the stats around total requests (downstream_rq_total_ & similar) will not be modified, as they are modified by ConnectionManagerImpl::ActiveStream. It seems like an invalid request should still be counted in those statistics.