net/mlx5: fix indexed pool fetch overlap

net/mlx5: fix indexed pool fetch overlap

For indexed pool with local cache, when a new trunk is allocated,
half of the trunk's index was fetched to the local cache. In case
of local cache size was less then half of the trunk size, memory
overlap happened.

This commit adds the check of the fetch size, if local cache size
is less than fetch size, adjust the fetch size to be local cache
size.

Fixes: d15c0946beea ("net/mlx5: add indexed pool local cache")
Cc: stable@dpdk.org
Signed-off-by: Suanming Mou <suanmingm@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>