Simplify reschedule points, mail works now!

kernel/syscall/syscall.c

@@ -108,7 +108,8 @@ DEFINE_SYSCALL (sys_argument_ptr) { return proc->uvaddr_argument; }
 
 /* int sched (void) */
 DEFINE_SYSCALL (sys_sched) {
-  reschedule_list_append (rctx, thiscpu);
+  rctx->reschedule = true;
+  rctx->cpu = thiscpu;
   return SYSRESULT (ST_OK);
 }