ftp: fix LIST, NLST and MLSD cmd-channel output

A recent patch, committed as b72f2b5283c7a1f3bdd7b7f2c7e5313802a1dff2,
added support for the delayed passive mode.  Unfortunately, it
also broke the LIST, NLST and MLSD output as it omits the 150
response for clients that use active mode.

Although our functional tests failed to detect the problem, Globus
(formally known as GlobusOnline) fails if the 150 message is missing.

This patch adds the missing message, fixing Globus

Request: 1.9
Patch: https://rb.dcache.org/r/7075/
Acked-by: Gerd Behrmann
Acked-by: Dmitry Litvintsev
Target: master
Require-notes: yes
Require-book: no