A read-only value that indicates the support of
operation of the 1000BASE-PX PHY optional FEC Sublayer
for Forward error correction see [802.3ah] clause 65.2).
unknown(1) value is assigned in initializing, for non
FEC support state or type not yet known. nonsupported(2)
value is assigned when Sublayer is not support.
supported(3) value is assigned when Sublayer is
supported.