Better handling of extensions in PiPipeconf

Now built using a URL, while input streams are generated on-demand.
Before it could happen that the input stream was completelly read by
someone, leaving it unusable by others.

Change-Id: I61a76bf8b8c1d2f6e2d987661025e0323d59e1c7
diff --git a/core/api/src/main/java/org/onosproject/net/pi/model/PiPipeconf.java b/core/api/src/main/java/org/onosproject/net/pi/model/PiPipeconf.java
index f94ae6e..389da5c 100644
--- a/core/api/src/main/java/org/onosproject/net/pi/model/PiPipeconf.java
+++ b/core/api/src/main/java/org/onosproject/net/pi/model/PiPipeconf.java
@@ -68,9 +68,9 @@
     boolean hasBehaviour(Class<? extends Behaviour> behaviourClass);
 
     /**
-     * Returns, if present, an input stream of ad device-specific or control
-     * protocol-specific extension of this configuration. For example, if requesting a
-     * target-specific P4 binary, this will return the same bytes produced by the P4 compiler.
+     * Returns, if present, an input stream pointing at the beginning of a file representing a device-specific or
+     * control protocol-specific extension of this configuration. For example, if requesting a target-specific P4
+     * binary, this will return the same bytes produced by the P4 compiler.
      *
      * @param type extension type
      * @return extension input stream