BpfNetMaps: do not register BpfNetMaps JNI before T

BpfNetMaps needs to go through netd before T and must *never* use the
JNI methods. BpfNetMaps already throws if this code path is called
before T.

Test: TH
Change-Id: I5f69c3673cfe86ef02f9b8e35a1db63f39c3da7e

service/jni/onload.cpp

@@ -38,11 +38,11 @@ extern "C" jint JNI_OnLoad(JavaVM* vm, void*) {
         return JNI_ERR;
     }
 
-    if (register_com_android_server_BpfNetMaps(env) < 0) {
-        return JNI_ERR;
-    }
-
     if (android::modules::sdklevel::IsAtLeastT()) {
+        if (register_com_android_server_BpfNetMaps(env) < 0) {
+            return JNI_ERR;
+        }
+
         if (register_com_android_server_connectivity_ClatCoordinator(env) < 0) {
             return JNI_ERR;
         }