init: create android::init:: namespace

With some small fixups along the way

Test: Boot bullhead
Test: init unit tests
Change-Id: I7beaa473cfa9397f845f810557d1631b4a462d6a
diff --git a/init/builtins.cpp b/init/builtins.cpp
index c78bec7..00ffbc3 100644
--- a/init/builtins.cpp
+++ b/init/builtins.cpp
@@ -67,6 +67,9 @@
 
 #define chmod DO_NOT_USE_CHMOD_USE_FCHMODAT_SYMLINK_NOFOLLOW
 
+namespace android {
+namespace init {
+
 static constexpr std::chrono::nanoseconds kCommandRetryTimeout = 5s;
 
 static int insmod(const char *filename, const char *options, int flags) {
@@ -924,3 +927,6 @@
     // clang-format on
     return builtin_functions;
 }
+
+}  // namespace init
+}  // namespace android