ice: Demote MTU change print to debug

commit bda5b7db upstream.

Following the changes of commit 12299132 ("net: ethernet: intel: Demote
MTU change prints to debug"), change the MTU change message to netdev_dbg()

Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Yongxin Liu <yongxin.liu@windriver.com>