net/failsafe: register as Rx interrupt mode

net/failsafe: register as Rx interrupt mode

This patch adds registering the Rx queues of the failsafe PMD with EAL
Rx interrupts subsystem.
Each failsafe RX queue is assigned with a unique eventfd and an enable
interrupts flag.
The PMD creates an interrupt vector containing the above eventfds and
Registers it with  EAL. The PMD also implements the Rx interrupts enable
and disable interface routines.
This patch does not implement the generation of Rx interrupts, so an
application can now wait for failsafe Rx interrupts but it will not
receive one.

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