Make end of frames for KSE thread, for system scope thread, without this

change, debugger will dump a weird stack backtrace.

sys/i386/i386/vm_machdep.c

@@ -441,6 +441,7 @@ cpu_set_upcall_kse(struct thread *td, struct kse_upcall *ku)
 	 * Set the trap frame to point at the beginning of the uts
 	 * function.
 	 */
+	td->td_frame->tf_ebp = 0; 
 	td->td_frame->tf_esp =
 	    (int)ku->ku_stack.ss_sp + ku->ku_stack.ss_size - 16;
 	td->td_frame->tf_eip = (int)ku->ku_func;