Fix unaligned load error on 32-bit architectures

On some 32-bit architectures, 64-bit atomic operations panic when the
value is not aligned properly.

In this package, this causes netConn operations to panic when compiling
with GOARCH=386, since netConn does atomic operations with int64 values
in the netConn struct (namely, with readExpired and writeExpired).

This commit fixes this by moving readExpired and writeExpired to the
beginning of the struct, which makes them properly aligned.

netconn.go

@@ -94,22 +94,23 @@ func NetConn(ctx context.Context, c *Conn, msgType MessageType) net.Conn {
 }
 
 type netConn struct {
+	readExpired  int64
+	writeExpired int64
+
 	c       *Conn
 	msgType MessageType
 
-	writeTimer   *time.Timer
-	writeMu      *mu
-	writeExpired int64
-	writeCtx     context.Context
-	writeCancel  context.CancelFunc
-
-	readTimer   *time.Timer
-	readMu      *mu
-	readExpired int64
-	readCtx     context.Context
-	readCancel  context.CancelFunc
-	readEOFed   bool
-	reader      io.Reader
+	writeTimer  *time.Timer
+	writeMu     *mu
+	writeCtx    context.Context
+	writeCancel context.CancelFunc
+
+	readTimer  *time.Timer
+	readMu     *mu
+	readCtx    context.Context
+	readCancel context.CancelFunc
+	readEOFed  bool
+	reader     io.Reader
 }
 
 var _ net.Conn = &netConn{}