app/testpmd: swap MAC in IEEE1588 forwarding

app/testpmd: swap MAC in IEEE1588 forwarding

IEEE1588 forwarding mode uses same port to receive and transmit packets.
In this mode, the MAC address in the packets are not touched,
and therefore, packets could be sent with the same destination
MAC address as the MAC address of the port that is transmitting,
which causes the packet to be dropped in some NICs.

In order to avoid this scenario, MAC addresses are swapped
before packet is sent out.

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>