samples: net: Provide DSA example to handle LLDP MGNT packets on ip_k66f

This patch brings simple example on per DSA port LLDP filtering based on
MAC address of received packet.

Each lan1, lan2 and lan3 ports handle separately LLDP packets going into
them.

Nonetheless, the K66F ENET handles correctly all other packets types -
to be more specific - ICMP, TCP/IP.

Setup -> ON HOST:

Configure/start the lldpd daemon (debian 10) on host to use
MAC 01:80:c2:00:00:03:
(lldpd -ddd & ) && sleep 2 && \
lldpcli configure lldp agent-type nearest-non-tpmr-bridge

Signed-off-by: Lukasz Majewski <lukma@denx.de>