I propose the following change to the sn/kernel arch SN IRQ handling.

The central issue here is that the current unidirectional list 
implementation in sn_irq_info does not easily allow sn_irq_info struct 
removals when PCI devices are hotplug removed from the system.

After input from a few others I changed my approach in the patch.  
Please reconsider it for submission to the community.

P.