MFC r329372 and r329464:
Implement enable_irq() and disable_irq() in the LinuxKPI and add checks for
valid IRQ tag before setting up or tearing down an interrupt handler in the
LinuxKPI. This is needed when the interrupt handler is disabled
before freeing the interrupt.

Submitted by: Johannes Lundberg <johalun0@gmail.com>
Sponsored by: Mellanox Technologies