cxgb3: detect mac link faults.

The driver currently ignores the local or remote link faults
raised at the mac layer. This patch fixes it.
Our mac however only advertizes link events, so wait for the
phy to stabilize the link, then enable mac link events interrupts.

Signed-off-by: Divy Le Ray <divy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>