Uncomment setting stack pointer to allow jumping into bootloader

stk500v2/main.cpp

@@ -605,7 +605,7 @@ void startup() __attribute__((naked, section(".vectors")));
 void startup()
 {
 	asm volatile("clr __zero_reg__");
-	// SP = RAMEND;
+	SP = RAMEND;
 	SREG = 0;
 	asm volatile("jmp main");
 }