clat: log if SIGKILL fails

This can fail on T due to lack of:
  https://android-review.googlesource.com/c/platform/system/sepolicy/+/2522976


  allow systemserver to sigkill clat

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I277213cff8dd4f2ce7ad5356e312c291da2c93eb

service/jni/com_android_server_connectivity_ClatCoordinator.cpp

@@ -500,7 +500,9 @@ static void stopClatdProcess(int pid) {
     if (ret == 0) {
         ALOGE("Failed to SIGTERM clatd pid=%d, try SIGKILL", pid);
         // TODO: fix that kill failed or waitpid doesn't return.
-        kill(pid, SIGKILL);
+        if (kill(pid, SIGKILL)) {
+            ALOGE("Failed to SIGKILL clatd pid=%d: %s", pid, strerror(errno));
+        }
         ret = waitpid(pid, &status, 0);
     }
     if (ret == -1) {