ixgbe: fix VF Rx/Tx function assignment

ixgbe: fix VF Rx/Tx function assignment

For the secondary process of DPDK to initialize ixgbevf, it will always
use the simple RX function or LRO RX function, and this behavior is not
the same RX/TX function selection logic as it is for the primary process.
Use the ixgbe_set_tx_function and ixgbe_set_rx_function to select the
RX/TX function when secondary process calls the init function for eth dev.

Fixes: 9d8a92628f21 ("ixgbe: remove simple scalar scattered Rx method")

Signed-off-by: Zhe Tao <zhe.tao@intel.com>
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Helin Zhang <helin.zhang@intel.com>