bus_teardown_intr does not work on nexus bus

Summary

To remove a registered interrupt handler from bus_setup_intr, I called the bus_teardown_intr function however the implementation of the teardown function for the nexus bus does install again the interrupt handler instead of removing it. This can be seen in the function nexus_teardown_intr at rtemsbsd/rtems/rtems-kernel-nexus.c.

The function probably should also free the cookie that nexus_setup_intr has allocated.