s/IMPL_HEADER/IMPL_INTERFACE/g

More appropriate name for this enum constant now that they are defined
in the interface source files.

Test: hidl_test
Change-Id: Ice531adb797c3213a2da18421b7e97fcfc888da3
diff --git a/Method.h b/Method.h
index 38f0dd2..229f042 100644
--- a/Method.h
+++ b/Method.h
@@ -36,7 +36,7 @@
 struct TypedVarVector;
 
 enum MethodImplType {
-    IMPL_HEADER,
+    IMPL_INTERFACE,
     IMPL_PROXY,
     IMPL_STUB, // overrides the code in onTransact; IMPL_STUB_IMPL will be ignored
     IMPL_STUB_IMPL, // use this->method() instead of mImpl->method()