devlink: Protect devlink port list traversal

Cited patch in fixes tag misses to protect port list traversal
while traversing per port reporter list.

Protect it using devlink instance lock.

Fixes: f4f54166

 ("devlink: Implement devlink health reporters on per-port basis")
Signed-off-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>