ocis: Cannot set mtime in file upload

Steps to reproduce

1. Upload a file with mtime timestamp for “Thu, 08 Aug 2019 04:18:13 GMT”

curl -XPUT https://135.181.40.111:9200/remote.php/webdav/file.txt einstein:relativity -d "hello" -H "X-OC-Mtime: 1565237893" -vk

1. Get the mtime with PROPFIND

Expected result

1. The mtime should match with the one set in the request

Actual result

1. The mtime is set automatically from upload time

❯ curl -XPROPFIND https://135.181.40.111:9200/remote.php/webdav/file.txt -u einstein:relativity -d '<?xml version="1.0"?>
                <d:propfind
                   xmlns:d="DAV:"
                   xmlns:oc="http://owncloud.org/ns"
                   xmlns:ocs="http://open-collaboration-services.org/ns"
                   > \
                    <d:prop><d:getetag/><d:getlastmodified/></d:prop>
                </d:propfind>'  -k | xmllint --format -
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   649  100   415  100   234    387    218  0:00:01  0:00:01 --:--:--   605
<?xml version="1.0" encoding="utf-8"?>
<d:multistatus xmlns:d="DAV:" xmlns:s="http://sabredav.org/ns" xmlns:oc="http://owncloud.org/ns">
  <d:response>
    <d:href>/remote.php/webdav/file.txt</d:href>
    <d:propstat>
      <d:prop>
        <d:getetag>"2452963196928:062c0215"</d:getetag>
        <d:getlastmodified>Fri, 11 Sep 2020 03:43:45 +0000</d:getlastmodified>
      </d:prop>
      <d:status>HTTP/1.1 200 OK</d:status>
    </d:propstat>
  </d:response>
</d:multistatus>