doc: Fix udebug -port bullet list

The formatting gets screwed up if we have multiple =item tags together
like this. To just have each one be a bullet point, just have a bare
=item before each one, without a "tag" or "key" for the =item.

Change-Id: I5cb7a98bd16f5999d529a42a0f822835f6d2f66e
Reviewed-on: http://gerrit.openafs.org/10388
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>