Add NO_FTPS [FTP] Option to disable FTPS support when necessary

Ideally, a sysop would never need to disable FTPS support, but as a trouble
shooting measure, it can be helpful.

src/sbbs3/ftpsrvr.c

@@ -2644,6 +2644,11 @@ static void ctrl_thread(void* arg)
 					sockprintf(sock,sess,"534 Already in TLS mode");
 					continue;
 				}
+				if(startup->options & FTP_OPT_NO_FTPS) {
+					lprintf(LOG_NOTICE, "%04d <%s> AUTH TLS rejected because FTPS support is disabled", sock, host_ip);
+					sockprintf(sock, sess, "431 TLS not available");
+					continue;
+				}
 				if (start_tls(&sock, &sess, TRUE) || sess == -1) {
 					lprintf(LOG_WARNING, "%04d <%s> failed to initialize TLS successfully", sock, host_ip);
 					break;

src/sbbs3/ftpsrvr.h

@@ -69,6 +69,7 @@ static struct init_field ftp_init_fields[] = {
 #define FTP_OPT_KEEP_TEMP_FILES		(1<<7)	/* Don't delete temp files (for debugging) */
 #define FTP_OPT_ALLOW_BOUNCE		(1<<8)
 #define FTP_OPT_LOOKUP_PASV_IP		(1<<9)	/* resolve public IP address for PASV response */
+#define FTP_OPT_NO_FTPS				(1<<10)	// Don't support START_TLS
 #define FTP_OPT_NO_HOST_LOOKUP		(1<<11)
 #define FTP_OPT_NO_RECYCLE			(1<<27)	/* Disable recycling of server		*/
 #define FTP_OPT_MUTE				(1U<<31)
@@ -89,6 +90,7 @@ static ini_bitdesc_t ftp_options[] = {
 	{ FTP_OPT_KEEP_TEMP_FILES		,"KEEP_TEMP_FILES"		},
 	{ FTP_OPT_ALLOW_BOUNCE			,"ALLOW_BOUNCE"			},
 	{ FTP_OPT_LOOKUP_PASV_IP		,"LOOKUP_PASV_IP"		},
+	{ FTP_OPT_NO_FTPS				,"NO_FTPS"				},
 	{ FTP_OPT_NO_HOST_LOOKUP		,"NO_HOST_LOOKUP"		},
 	{ FTP_OPT_NO_RECYCLE			,"NO_RECYCLE"			},
 	{ FTP_OPT_MUTE					,"MUTE"					},