Support data channel encryption

[novicov]

When I use TLS channel encryption on my FTP (IIS host), I have error: [534 Policy requires SSL.].
LOG: ```

FTP: Connecting from host []
FTP: Connecting with configuration [] ...
220 Microsoft FTP Service
AUTH TLS
234 AUTH command ok. Expecting TLS Negotiation.
FTP: Logging in, command printing disabled
FTP: Logged in, command printing enabled
CWD /
250 CWD command successful.
TYPE A
200 Type set to A.
CWD /
250 CWD command successful.
FEAT
211-Extended features supported:
LANG EN
UTF8
AUTH TLS;TLS-C;SSL;TLS-P;
PBSZ
PROT C;P;
CCC
HOST
SIZE
MDTM
REST STREAM
211 END
SYST
215 Windows_NT
PORT 92,62,112,13,197,31
200 PORT command successful.
LIST -a
534 Policy requires SSL.
CWD /
250 CWD command successful.
CWD Areas/HelpPage
250 CWD command successful.
PORT 92,62,112,13,197,33
200 PORT command successful.
STOR HelpPage.css
534 Policy requires SSL.
FTP: Disconnecting configuration [****] ...
ERROR: Exception when publishing, exception message [Could not write file. Server message: [534 Policy requires SSL.]]

[bjmi]

Same error pattern with FileZilla Server and explicit TLS enabled:

FTP: Connecting from host [...]
FTP: Connecting with configuration [...] ...
220 Welcome
AUTH TLS
234 Using authentication type TLS
FTP: Logging in, command printing disabled
FTP: Logged in, command printing enabled
CWD /
250 CWD successful. "/" is current directory.
TYPE I
200 Type set to I
CWD /
250 CWD successful. "/" is current directory.
CWD RemoteDir
250 CWD successful. "/RemoteDir" is current directory.
PASV
227 Entering Passive Mode (a,b,c,d,242,122)
STOR artifacts.jar
521 PROT P required
FTP: Disconnecting configuration [...] ...
ERROR: Exception when publishing, exception message [Could not write file. Server message: [521 PROT P required
]]