Declare main in global NS, without extern "C"

The C++ standard doesn't allow a linkage-specification for main,
https://eel.is/c++draft/basic.start.main#3.sentence-5:

"The main function shall not be declared with a linkage-specification
([dcl.link])."

Bug: http://b/379133546
Test: m android.hardware.automotive.can-service \
    android.hardware.macsec-service \
    canhalconfigurator-aidl
Change-Id: Ifbc36bc1e3e05e6a12153d371871f4168bbe4cf8

diff --git a/macsec/aidl/default/service.cpp b/macsec/aidl/default/service.cpp
index faf3a09..9d5d3bf 100644
--- a/macsec/aidl/default/service.cpp
+++ b/macsec/aidl/default/service.cpp
@@ -20,12 +20,11 @@
 #include <android/binder_manager.h>
 #include <android/binder_process.h>
 
-namespace android::hardware::macsec {
-
 using namespace std::string_literals;
+using namespace android;
 using ::aidl::android::hardware::macsec::MacsecPskPlugin;
 
-extern "C" int main() {
+int main() {
     base::SetDefaultTag("MacsecPskPlugin");
     base::SetMinimumLogSeverity(base::VERBOSE);
 
@@ -40,4 +39,3 @@
     LOG(FATAL) << "MacsecPskPlugin exited unexpectedly!";
     return EXIT_FAILURE;
 }
-}  // namespace android::hardware::macsec