app/test: add unit tests for link bonding mode 6

app/test: add unit tests for link bonding mode 6

Added 4 unit tests checking link bonding mode 6 behavior.

Also modified virtual_pmd so it is possible to provide packets,
that should be received with rx_burst and to inspect packets
transmitted by tx_burst.

In packet_burst_generator.c function creating eth_header is
modified, so it accepts ether_type as a parameter and function
creating arp_header is added. Updated other unit tests to get
rid of compilation errors.

Signed-off-by: Maciej Gajdzica <maciejx.t.gajdzica@intel.com>
Acked-by: Declan Doherty <declan.doherty@intel.com>