net/ixgbe/base: allow per-device-type method calls
net/ixgbe/base: allow per-device-type method calls

Use the method pointers instead of direct function calls for IOSF
access so that the right functions can be called on X550EM_a,
compared to other devices using the driver.

Signed-off-by: Beilei Xing <7fb7e49de6d75fb4140bfcdada52e66859d93ebd@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk