net/mlx5: fix memory event callback list

net/mlx5: fix memory event callback list

The shared Infiniband device context should be included
into memory event callback list only once on context creation,
and removed from the list only once on context destroying.
Multiple insertions of the same object caused the infinite
loop on the list processing.

Fixes: ccb3815346e6 ("net/mlx5: update memory event callback for shared context")
Cc: stable@dpdk.org
Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>