cxgb4: Restore L1 cfg, if FW rejects new L1 cfg settings

In the ethtool set_settings() routine we need to remember our old L1
Configuration in case the firmware rejects the request and then restore
that.

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>