ixgbe: cleanup functions that should have been defined static

We have some ~40 functions that were being called out with 'make
namespacecheck'.  This patch changes these functions to be static.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>