sources: Fix ifdefs

We don't want to compare the boolean value of these macros, but the
existence of their definition. None of our Makefile definitions define
an actual value for them, but rely on their presence.

Change-Id: I21688d70acfbfef4d8ca3284fd6db8dbf64b7e6f
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/network_manager.cpp b/network_manager.cpp
index 881b767..751d1a1 100644
--- a/network_manager.cpp
+++ b/network_manager.cpp
@@ -210,7 +210,7 @@
     restartTimers();
 }
 
-#if SYNC_MAC_FROM_INVENTORY
+#ifdef SYNC_MAC_FROM_INVENTORY
 void Manager::setFistBootMACOnInterface(
     const std::pair<std::string, std::string>& inventoryEthPair)
 {