MFC r355107 and r355597.

r355107:
cxgbe(4): Allow the driver to specify multiple FECs that the firmware
should try in order to link up with the peer.

Various FEC variables within the driver can now have multiple bits set
instead of being powers of 2. 0 and -1 in the user knobs still mean no
FEC and auto (driver decides) respectively for backward compatibility,
but no-FEC and auto now have their own bits in the internal
representation. There is a new bit that can be set to request the FEC
recommended by the cable/transceiver module.

Add sysctls to display link related capabilities of the local side as
well as the link partner.

Note that all this needs a new firmware and the documentation for the
driver FEC knobs will be updated after that firmware is added to the
driver.

r355597:
cxgbe(4): Man page updates to go with r355107.

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