This patch does a few things.

1) Makes /sys/bus/fcoe/ctlr_{create,destroy} interfaces.
   These interfaces take an <ifname> and will either
   create an FCoE Controller or destroy an FCoE
   Controller depending on which file is written to.

   The new FCoE Controller will start in a DISABLED
   state and will not do discovery or login until it
   is ENABLED. This pause will allow us to configure
   the FCoE Controller before enabling it.

2) Makes the 'mode' attribute of a fcoe_ctlr_device
   writale. This allows the user to configure the mode
   in which the FCoE Controller will start in when it
   is ENABLED.

   Possible modes are 'Fabric', or 'VN2VN'.

   The default mode for a fcoe_ctlr{,_device} is 'Fabric'.
   Drivers must implement the set_fcoe_ctlr_mode routine
   to support this feature.

   libfcoe offers an exported routine to set a FCoE
   Controller's mode. The mode can only be changed
   when the FCoE Controller is DISABLED.

   This p...