net/mlx5: fix flow age event triggering

net/mlx5: fix flow age event triggering

A FLOW_AGE event should be invoked when a new aged-out flow is detected
by the PMD after the last user get-aged query calling.
The PMD manages 2 flags for this information and check them in order to
decide if an event should be invoked:
MLX5_AGE_EVENT_NEW - a new aged-out flow was detected. after the last
check.
MLX5_AGE_TRIGGER - get-aged query was called after the last aged-out
flow.
The 2 flags were unset after the event invoking.

When the user calls get-aged query from the event callback, the TRIGGER
flag was set inside the user callback and unset directly after the
callback what may stop the event invoking forever.

Unset the TRIGGER flag before the event invoking in order to allow set
it by the user callback.

Fixes: f935ed4b645a ("net/mlx5: support flow hit action for aging")
Cc: stable@dpdk.org
Reported-by: David Bouyeure <david.bouyeure@fraudbuster.mobi>
Signed-off-by: Michael Baum <michaelba@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>