net/mlx5e: Fix build break when CONFIG_XPS is not set

mlx5e_accel_sk_get_rxq is only used in ktls_rx.c file which already
depends on XPS to be compiled, move it from the generic en_accel.h
header to be local in ktls_rx.c, to fix the below build break

In file included from
../drivers/net/ethernet/mellanox/mlx5/core/en_main.c:49:0:
../drivers/net/ethernet/mellanox/mlx5/core/en_accel/en_accel.h:
In function ‘mlx5e_accel_sk_get_rxq’:
../drivers/net/ethernet/mellanox/mlx5/core/en_accel/en_accel.h:153:12:
error: implicit declaration of function ‘sk_rx_queue_get’ ...
  int rxq = sk_rx_queue_get(sk);
            ^~~~~~~~~~~~~~~

Fixes: 1182f365 ("net/mlx5e: kTLS, Add kTLS RX HW offload support")
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>