ixgbe: declare functions as static

Following patch fixes warnings reported by `make namespacecheck`

Reported by Stephen Hemminger

CC: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Stephen Ko <stephen.s.ko@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>