net/mlx5: split flow counter struct

net/mlx5: split flow counter struct

Currently, the counter struct saves both the members used by batch
counters and none batch counters. The members which are only used
by none batch counters cost 16 bytes extra memory for batch counters.
As normally there will be limited none batch counters, mix the none
batch counter and batch counter members becomes quite expensive for
batch counter. If 1 million batch counters are created, it means 16 MB
memory which will not be used by the batch counters are allocated.

Split the mlx5_flow_counter struct for batch and none batch counters
helps save the memory.

Signed-off-by: Suanming Mou <suanmingm@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>