A read-write value that indicates the mode of operation
of the 1000BASE-PX PHY optional FEC Sublayer for Forward
error correction see [802.3ah] clause 65.2).
A GET operation returns the current mode of operation
the PHY. A SET operation changes the mode of operation
of the PHY to the indicated value. unknown(1) value is
assigned in initializing, for non FEC support state or
type not yet known. disabled(2) value is assigned when
Sublayer operating in disabled mode. enabled(3) value is
assigned when Sublayer operating in FEC mode. writing
can be done all the time.