cmd/observe: fix stdin reading from file redirection

The `hubble observe` command could only read from stdin when being piped
to, e.g. `cat sample.json | hubble observe` but not via file redirect
such as `hubble observe < sample.json`. This commit makes the latter
possible.

Signed-off-by: Robin Hahling <robin.hahling@gw-computing.net>

cmd/observe/flows.go

@@ -180,7 +180,7 @@ more.`,
 			if err != nil {
 				return err
 			}
-			if fi.Mode()&os.ModeNamedPipe != 0 {
+			if fi.Mode()&os.ModeCharDevice == 0 {
 				// read flows from stdin
 				client = newIOReaderObserver(os.Stdin)
 				logger.Logger.Debug("Reading flows from stdin")