fcoe: Declare fcoe_ctlr_mode_set() static

The function fcoe_ctlr_mode_set() is local, hence declare it static.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>