init: Add gentle_kill service property

If a service specifies gentle_kill, attempt to stop it will send SIGTERM
instead of SIGKILL. After 200ms, it will issue a SIGKILL.

Bug: 249043036
Test: atest CtsInitTestCases:init#GentleKill
      Added in next patch
Change-Id: Ieb0e4e24d31780aca1cf291f9d21d49cee181cf2
diff --git a/init/service.h b/init/service.h
index f9749d2..3ef8902 100644
--- a/init/service.h
+++ b/init/service.h
@@ -56,6 +56,8 @@
                                      // should not be killed during shutdown
 #define SVC_TEMPORARY 0x1000  // This service was started by 'exec' and should be removed from the
                               // service list once it is reaped.
+#define SVC_GENTLE_KILL 0x2000  // This service should be stopped with SIGTERM instead of SIGKILL
+                                // Will still be SIGKILLed after timeout period of 200 ms
 
 #define NR_SVC_SUPP_GIDS 12    // twelve supplementary groups