set ENABLE_GOOGLE to boolean definition

ENABLE_GOOGLE was set as an if defined.  Change it to a true boolean so
it can be defined as 0 or 1 and will be have as expected.

Change-Id: I2bf59019ede669679ece6a7fbe7cf4b57c07102b
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/main.cpp b/main.cpp
index edac802..0f9bcad 100644
--- a/main.cpp
+++ b/main.cpp
@@ -178,7 +178,7 @@
 {
     oem::Router* oemRouter = oem::mutableRouter();
 
-#ifdef ENABLE_GOOGLE
+#if ENABLE_GOOGLE
     /* Install in Google OEM Namespace when enabled. */
     std::fprintf(stderr,
                  "Registering OEM:[%#08X], Cmd:[%#04X] for Ethstats Commands\n",