net/failsafe: add Rx interrupts

net/failsafe: add Rx interrupts

This patch is the last patch in the series of patches aimed
to add support for registering and waiting for Rx interrupts
in failsafe PMD. This allows applications to wait for Rx events
from the PMD using the DPDK rte_epoll subsystem.
The failsafe PMD presents to the application a facade of a single
device to be handled by the application while internally it manages
several devices on behalf of the application including packets
transmission and reception.
The Proposed failsafe Rx interrupt scheme follows this approach.
The failsafe PMD will present the application with a single set of
Rx interrupt vectors representing the failsafe Rx queues, while
internally it will serve as an interrupt proxy for its subdevices.
will allow applications to wait for Rx traffic from the failsafe
PMD by registering and waiting for Rx events from its Rx queues.
In order to support this the following is suggested:
  * Every Rx queue in the failsafe (virtual) device will be assigned
  * a Linux event file descriptor (efd) and an enable_interrupts flag.
  * The failsafe PMD will fill in its rte_intr_handle structure with
    the Rx efds assigned previously and register them with the EAL.
  * The failsafe driver will create a private epoll fd (epfd) and
  * will allocate enough space to handle all the Rx events from all its
    subdevices.
  * Acting as an application,
    for each Rx queue in each active subdevice the failsafe will:
      o Register the Rx queue with the EAL.
      o Pass the EAL the failsafe private epoll fd as the epfd to
        register the Rx queue event on.
      o Pass the EAL, as a parameter, the pointer to the failsafe Rx
        queue that handles this Rx queue.
      o Using the DPDK service callbacks, the failsafe PMD will launch
        an Rx proxy service that will Wait on the epoll fd for Rx
        events from the sub-devices.
      o For each Rx event received the proxy service will
          - Retrieve the pointer to failsafe Rx queue that handles
            this subdevice Rx queue from the user info returned by the
            EAL.
          - Trigger a failsafe Rx event on that queue by writing to
            the event fd unless interrupts are disabled for that queue.
  * The failsafe pmd will also implement the rx_queue_intr_enable
  * and rx_queue_intr_disable routines that will enable and disable Rx
    interrupts respectively on both on the failsafe and its subdevices.

Signed-off-by: Moti Haimovsky <motih@mellanox.com>
Acked-by: Gaetan Rivet <gaetan.rivet@6wind.com>