I observed that setting --max-pkt-len to a value lower than 1500 does not
enforce this value even though "show port info X" showed that the MTU was set
to the value passed in.

(e.g. packets larger than 800 bytes (> 1000 bytes) were still observed even
though --max-pkt-len=800 was set)

I believe that there is a default value that --max-pkt-len falls back on if the
value is too low. If this is the case, this value should also be reflected in
the port info.