ice: Add missing case in print_link_msg for printing flow control

Currently we aren't checking for the ICE_FC_NONE case for the current
flow control mode. This is causing "Unknown" to be printed for the
current flow control method if flow control is disabled. Fix this by
adding the case for ICE_FC_NONE to print "None".

Signed-off-by: Brett Creeley <brett.creeley@intel.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>