Add a message for EOF-related broken pipe errors

It's quite confusing from production logs when all I get is
"broken pipe" and I don't know which path was taken for that error
to be logged.

Author: nox

src/proto/streams/state.rs

@@ -303,7 +303,10 @@ impl State {
             Closed(..) => {}
             ref state => {
                 tracing::trace!("recv_eof; state={:?}", state);
-                self.inner = Closed(Cause::Error(io::ErrorKind::BrokenPipe.into()));
+                self.inner = Closed(Cause::Error(io::Error::new(
+                    io::ErrorKind::BrokenPipe,
+                    "stream closed because of broken pipe",
+                ).into()));
             }
         }
     }

src/proto/streams/streams.rs

@@ -807,7 +807,13 @@ impl Inner {
         let send_buffer = &mut *send_buffer;
 
         if actions.conn_error.is_none() {
-            actions.conn_error = Some(io::Error::from(io::ErrorKind::BrokenPipe).into());
+            actions.conn_error = Some(
+                io::Error::new(
+                    io::ErrorKind::BrokenPipe,
+                    "connection closed because of broken pipe",
+                )
+                .into(),
+            );
         }
 
         tracing::trace!("Streams::recv_eof");