fw: rename BroadcastStrategy to MulticastStrategy

BroadcastStrategy is temporarily retained for backwards compatibility.

This commit also updates nfd.conf and ndn-autoconfig to use MulticastStrategy
in place of BroadcastStrategy.

refs #3011

Change-Id: I011f1cf75db26b3c93552f8322a0bba4ce8dd033
diff --git a/nfd.conf.sample.in b/nfd.conf.sample.in
index fa229b4..65d9def 100644
--- a/nfd.conf.sample.in
+++ b/nfd.conf.sample.in
@@ -54,9 +54,9 @@
   strategy_choice
   {
     /               /localhost/nfd/strategy/best-route
-    /localhost      /localhost/nfd/strategy/broadcast
+    /localhost      /localhost/nfd/strategy/multicast
     /localhost/nfd  /localhost/nfd/strategy/best-route
-    /ndn/broadcast  /localhost/nfd/strategy/broadcast
+    /ndn/broadcast  /localhost/nfd/strategy/multicast
   }
 }