ftp: Close passive port on failure

globus-url-copy hangs on proxied passive mode connections for which
the mover is killed. Although the proxy adapter is shut down and an
error is reported on the control channel, the fact that the server
socket for the passive mode is not closed and thus has an unaccepted
connection causes globus-url-copy to hang.

This patch closes the passive port on transfer failure. The mode state
is set to an invalid state to force the client to reset the data
channel using either PORT or PASV (or one of the variations).

I am not request backport further than 2.9 as I expect that we will
soon backport the entire door to get delayed passive and IPv6 functionality
in older releases.

Target: trunk
Request: 2.9
Require-notes: yes
Require-book: no
Acked-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Patch: https://rb.dcache.org/r/7079/