Provide a knob to control per-VF Tx switching feature by adding a config
option, CONFIG_RTE_LIBRTE_QEDE_VF_TX_SWITCH. By default, it will be kept
in disabled state for better performance with small sized frames.
Fixes: 2ea6f76aff40 ("qede: add core driver")
Cc: stable@dpdk.org
Signed-off-by: Harish Patil <harish.patil@cavium.com>