On dcbnl callback getpgtccfgtx, the driver should check the ets
capability before ets query command is sent to firmware.
It is valid to return from this void function without changing in/out
parameters, as these parameters are initialized to
DCB_ATTR_VALUE_UNDEFINED.

Fixes: 3a6a931d ("net/mlx5e: Support DCBX CEE API")
Signed-off-by: Moshe Shemesh <moshe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>