pcilmr: Ensure that utility can accept either Downstream or Upstream link port

pcilmr: Ensure that utility can accept either Downstream or Upstream link port

Previously, the utility expected only the Upstream Port to be input and,
in fact, passing the Downstream Port led to strange and buggy error
messages. Improve arguments parsing logic to accept any side of the link.

It seems that the only use case that will not be available now is margining
the internal links of the switch, but this scenario looks as strange as
possible.

Signed-off-by: Nikita Proshkin <n.proshkin@yadro.com>