[SCSI] fcoe: move link speed checking into its own routine

It doesn't make sense to update the link speed in the is_link_ok()
routine. Move it to it's own routine and acquire the device speed
when we're configuring the device initially as well as if there are
any netdev events received.

Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>