smb: set the share comment as UDS_COMMENT for the UI to display

Summary:
currently this seems to not really have any visibility through dolphin
so concluding the fix also requires changes to dolphin to enable the
comment somewhere. it is technically a column in the details view but
that doesn't actually seem to work

CCBUG: 105086

Test Plan: hoping for the best in absence of a UI!

Reviewers: ngraham

Subscribers: kde-frameworks-devel, kfm-devel

Tags: #dolphin, #frameworks

Differential Revision: https://phabricator.kde.org/D27292