net: aquantia: synchronized flow control between mac/phy

Flow control statuses were not synchronized between blocks,
that caused packets/link drop on some corner cases, when
MAC sent PFC although Phy was not expecting these to come.

Driver should readout the negotiated FC from phy and
configure RX block accordigly.

This is done on each link change event with information from FW.

Fixes: 288551de

 ("net: aquantia: Implement rx/tx flow control ethtools callback")
Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>