Some apps like VPP use PASSTHRU+MARK flow rules to offload packet
matching to the NIC. Just like MARK+RSS used by OVS-DPDK and others,
PASSTHRU+MARK is used to "mark and then receive normally". Recent VIC
adapters support such flow rules, so enable PASSTHRU for this limited
use case.
Signed-off-by: Hyong Youb Kim <hyonkim@cisco.com>