fw: delegate sending Nack-Duplicate to forwarding strategy

This commit introduces a new strategy trigger (onInterestLoop) that
is invoked when a duplicate Interest is received. The default behavior
of the new trigger is to send a Nack as before. We also modify the
MulticastStrategy to override onInterestLoop and skip sending the Nack.

Refs: #5278
Co-authored-by: Davide Pesavento <davidepesa@gmail.com>
Change-Id: I07bb520bd31cbfc8d8f8581e05c49927f8ea35f7
diff --git a/daemon/fw/multicast-strategy.cpp b/daemon/fw/multicast-strategy.cpp
index 08eda9a..85b0535 100644
--- a/daemon/fw/multicast-strategy.cpp
+++ b/daemon/fw/multicast-strategy.cpp
@@ -53,7 +53,7 @@
 const Name&
 MulticastStrategy::getStrategyName()
 {
-  static const auto strategyName = Name("/localhost/nfd/strategy/multicast").appendVersion(4);
+  static const auto strategyName = Name("/localhost/nfd/strategy/multicast").appendVersion(5);
   return strategyName;
 }