stop decoding immediatly after first null byte
decode hex-encoded strings in LLDP info

see: #2670,#2746,#2754
decode hex-encoded strings in CDP info

see: #2670,#2746,#2754
don't duplicate remote mac address uselessly
ignore empty sysname value in LLDP info
ignore empty ifdescr value in LLDP info
skip earlier if required