[contrib] Enable bochs debug port by default

Signed-off-by: Michael Brown <mcb30@ipxe.org>

contrib/vm/bochsrc.txt

 # Example:
 #   port_e9_hack: enabled=1
 #=======================================================================
-#port_e9_hack: enabled=1
+port_e9_hack: enabled=1
 
 #=======================================================================
 # DEBUG_SYMBOLS: