Bug 34961: Add sort parameter to OPAC search results RSS feed link

Bug 34961: Add sort parameter to OPAC search results RSS feed link

This patch corrects two RSS links in the OPAC search results template so
that they include the correct parameters, including the descending sort
by acquisition date.

To test, apply the patch and go to the OPAC.

- Perform a catalog search which will return search results.
- Next to the page heading "Your search returned X results" is an RSS
  link. Check the link to confirm that it has all the expected
  parameters:

  opac-search.pl?idx=kw&q=nude&count=50&sort_by=acqdate_dsc&format=rss

- Perform a search which will return no results and check the RSS link
  on that page. It should be the same.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 1f730fb8665a53457ad709933d3518577c041a6e)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>