Update license in source code to be Apache 2

Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>
diff --git a/src/cc/b_frontend_action.cc b/src/cc/b_frontend_action.cc
index 512da65..b299958 100644
--- a/src/cc/b_frontend_action.cc
+++ b/src/cc/b_frontend_action.cc
@@ -1,3 +1,18 @@
+/*
+ * Copyright (c) 2015 PLUMgrid, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
 #include <linux/bpf.h>
 
 #include <clang/AST/ASTConsumer.h>