p2p: interrupt MsgPipe payload read/write

This is better because protocols might not actually read the payload for
some errors (msg too big, etc.) which can be a pain to test with the old
behaviour.

p2p/message.go

@@ -185,7 +185,10 @@ func (p *MsgPipeRW) WriteMsg(msg Msg) error {
 		case p.w <- msg:
 			if msg.Size > 0 {
 				// wait for payload read or discard
-				<-consumed
+				select {
+				case <-consumed:
+				case <-p.closing:
+				}
 			}
 			return nil
 		case <-p.closing:
@@ -207,8 +210,8 @@ func (p *MsgPipeRW) ReadMsg() (Msg, error) {
 }
 
 // Close unblocks any pending ReadMsg and WriteMsg calls on both ends
-// of the pipe. They will return ErrPipeClosed. Note that Close does
-// not interrupt any reads from a message payload.
+// of the pipe. They will return ErrPipeClosed. Close also
+// interrupts any reads from a message payload.
 func (p *MsgPipeRW) Close() error {
 	if atomic.AddInt32(p.closed, 1) != 1 {
 		// someone else is already closing