lp: change return of LpPacket::wireEncode() to non-const

refs #3324

Change-Id: I0b178bc59f8107a947f5f500d7db4cdb9c1e2596
diff --git a/src/lp/packet.hpp b/src/lp/packet.hpp
index aa77a4f..bc35122 100644
--- a/src/lp/packet.hpp
+++ b/src/lp/packet.hpp
@@ -55,7 +55,7 @@
   /**
    * \brief encode packet into wire format
    */
-  const Block
+  Block
   wireEncode() const;
 
   /**