Internally TAP device appears to be using priority as TC index. Which leads to
the following buggy behavior. Drivers should allow multiple flow rules with
same priority.

testpmd> flow create 0 priority 2 ingress pattern eth src is 06:05:04:03:02:01
/ end actions queue index 2 / end
Flow rule #0 created
testpmd> flow create 0 priority 2 ingress pattern eth src is 06:05:04:03:02:00
/ end actions queue index 3 / end
tap_nl_dump_ext_ack(): Filter already exists
tap_flow_create(): Kernel refused TC filter rule creation (17): File exists
port_flow_complain(): Caught PMD error type 2 (flow rule (handle)): overlapping
rules or Kernel too old for flower support: File exists