linux-phytec-ti

igc: Add flow control support

This change adds flow control settings. This is required to
enable the legacy flow control support.

Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>