net/mlx5e: Check support before TC swap in ETS init

Should not do the following swap between TCs 0 and 1
when max num of TCs is 1:
tclass[prio=0]=1, tclass[prio=1]=0, tclass[prio=i]=i (for i>1)

Fixes: 08fb1dac ("net/mlx5e: Support DCBNL IEEE ETS")
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>