Software FCOE on Intel Ethernet Converged Network Adapter X520 Series and X540 Series products are recommended to use ixgbe driver versions 3.7 (inbox) or 3.21.4.3 (async) on VMware ESXi 5.5 and ESXi 6.0.
Software FCoE on X550 based adapters is not supported at this time by any existing ixgbe driver version. Intel intends to have a fix available for VMware ESXi 6.0 in Q3, 2017. No fix is planned for ESXi 5.5.
Software FCoE is no longer supported on Intel 10Gb products on VMware ESXi 6.5.