net/cxgbe: update link Forward Error Correction (FEC)

net/cxgbe: update link Forward Error Correction (FEC)

Normally, firmware reads various Forward Error Correction parameters
from a Transceiver Module i2c EPROM and uses a couple of IEEE Standards
(802.3bj for 100Gb/s and 802.3by for 25Gb/s) to interpret those
parameters and come up with supported and default FEC settings.
Firmware then sends these FEC parameters to the Host Driver which gives
the Host Administrator an opportunity to change them if necessary in
order to establish a Link with a Switch which may have made a
non-standard FEC decision.

This commit recognizes "auto" as a discrete FEC mode which can be
used to explicitly select the IEEE 802.3 standard based FEC selection.

Original work by Surendra Mobiya <surendra@chelsio.com>

Signed-off-by: Kumar Sanghvi <kumaras@chelsio.com>
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>