net/mlx5e: Use the correct pause values for ethtool advertising

Query the operational pause from firmware (PFCC register) instead of
always passing zeros.

Fixes: 665bc539

 ("net/mlx5e: Use new ethtool get/set link ksettings API")
Signed-off-by: Gal Pressman <galp@mellanox.com>
Cc: kernel-team@fb.com
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>