Move "query queue counter out of buffer" helper function out of
qp.c to en_main.c, since mlx5e netdev driver is the only one to use it.

Also allocate the output buffer on the stack instead of the heap, to reduce
number of heap allocs on update_stats work.
Signed-off-by: Gal Pressman <galp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Cc: kernel-team@fb.com