net/mlx5e: Check ets capability before initializing ets settings

During the initial setup, the ets command is sent to firmware
without checking if the HCA supports ets. This causes the invalid
command error. Add the ets capiblity check before sending firmware
command to initialize ets settings.

Fixes: e207b7e9 ("net/mlx5e: ConnectX-4 firmware support for DCBX")
Signed-off-by: Huy Nguyen <huyn@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>