add inventory tests
function transfer
canonicalise memory too
more consistency for function names
handle value canonicalisation in caller
use less strict patterns

0:0:0:0:0:0 is also a valid mac address, as bytes are not mandatorily
0-padded.
fix mac address handling

The multiple kind of values for mac addresses don't come from 'bad'
OIDs, rather from the fact than they may be encoded either as plain
strings, either as hex-strings, and Net::SNMP automatically tries to
translates them in the second case. See
https://rt.cpan.org/Public/Bug/Display.html?id=1946 for details.
handle value canonicalisation in caller
fix expected results
avoid spurious warnings