Implement the INTR_EPOCH flag to request a subsystem specific EPOCH(9) to protect the software interrupt handler. This change basically reverts r357004, but provides the same functionality.
This change also allows interrupt handlers to opt out from automatic EPOCH(9) protection, typically drivers which are implemented via the LinuxKPI or in case the interrupt handler is frequently invoked w/o actually generating any packets for network processing.
Sponsored by: Mellanox Technologies