net/iavf: fix function pointer in multi-process

net/iavf: fix function pointer in multi-process

This patch uses the index value to call the function, instead of the
function pointer assignment to save the selection of Receive Flex
Descriptor profile ID.

Otherwise the secondary process will run with wrong function address
from primary process.

Fixes: 12b435bf8f2f ("net/iavf: support flex desc metadata extraction")
Cc: stable@dpdk.org
Signed-off-by: Steve Yang <stevex.yang@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>