Downstream Port Containment (DPC)

The relevant changes are presently in

• sys/dev/pci/pci-pci.c
• sys/dev/pci/pcireg.h
• sys/dev/pci/pcib_private.h

The sysctl dev.pcib.N.software_trigger_dpc can be used to synthesize a DPC event, if the switch/bridge allows it.

TODO

• Taskqueue thread needs to be created and interrupt work moved to it.
• Teardown code is needed
• It's unclear yet if DPC, HP, and AEN can share an MSI/MSIX vector.