A final(?) effort to reduce memory usage per flow (#1389)

Remove some unused fields and re-organize other ones.
In particular:
* Update the parameters of `ndpi_ssl_version2str()` function
* Zattoo, Thunder: these timestamps aren't really used.
* Ftp/mail: these protocols are dissected only over TCP.
* Attention must be paid to TLS.Bittorrent flows to avoid invalid
read/write to `flow->protos.bittorrent.hash` field.

This is the last(?) commit of a long series (see 22241a1d, 227e586e,
730c2360, a8ffcd8b) aiming to reduce library memory consumption.

Before, at nDPI 4.0 (more precisly, at a6b10cf7, because memory stats
were wrong until that commit):
```
nDPI Memory statistics:
	nDPI Memory (once):      221.15 KB
	Flow Memory (per flow):  2.94 KB
```
Now:
```
nDPI Memory statistics:
	nDPI Memory (once):      231.71 KB
	Flow Memory (per flow):  1008 B       <---------
```
i.e. memory usage per flow has been reduced by 66%, dropping below the
psychological threshold of 1 KB.

To further reduce this value, we probably need to look into #1279:
let's fight this battle another day.

1 files changed, 11 insertions, 11 deletions

diff --git a/src/lib/protocols/ftp_control.c b/src/lib/protocols/ftp_control.c
index 2b6f1396f..81e475041 100644
--- a/src/lib/protocols/ftp_control.c
+++ b/src/lib/protocols/ftp_control.c
@@ -50,23 +50,23 @@ static int ndpi_ftp_control_check_request(struct ndpi_detection_module_struct *n
 #endif
 
   if(ndpi_match_strprefix(payload, payload_len, "USER")) {
-    ndpi_user_pwd_payload_copy((u_int8_t*)flow->ftp_imap_pop_smtp.username,
-			       sizeof(flow->ftp_imap_pop_smtp.username), 5,
+    ndpi_user_pwd_payload_copy((u_int8_t*)flow->l4.tcp.ftp_imap_pop_smtp.username,
+			       sizeof(flow->l4.tcp.ftp_imap_pop_smtp.username), 5,
 			       payload, payload_len);
     ndpi_set_risk(ndpi_struct, flow, NDPI_CLEAR_TEXT_CREDENTIALS);
     return 1;
   }
 
   if(ndpi_match_strprefix(payload, payload_len, "PASS")) {
-    ndpi_user_pwd_payload_copy((u_int8_t*)flow->ftp_imap_pop_smtp.password,
-			       sizeof(flow->ftp_imap_pop_smtp.password), 5,
+    ndpi_user_pwd_payload_copy((u_int8_t*)flow->l4.tcp.ftp_imap_pop_smtp.password,
+			       sizeof(flow->l4.tcp.ftp_imap_pop_smtp.password), 5,
 			       payload, payload_len);
     return 1;
   }
 
   if(ndpi_match_strprefix(payload, payload_len, "AUTH") ||
      ndpi_match_strprefix(payload, payload_len, "auth")) {
-    flow->ftp_imap_pop_smtp.auth_found = 1;
+    flow->l4.tcp.ftp_imap_pop_smtp.auth_found = 1;
     return 1;
   }
   /* ***************************************************** */
@@ -562,14 +562,14 @@ static int ndpi_ftp_control_check_response(struct ndpi_flow_struct *flow,
   case '2':
   case '3':
   case '6':
-    if(flow->ftp_imap_pop_smtp.auth_found == 1)
-      flow->ftp_imap_pop_smtp.auth_tls = 1;
+    if(flow->l4.tcp.ftp_imap_pop_smtp.auth_found == 1)
+      flow->l4.tcp.ftp_imap_pop_smtp.auth_tls = 1;
     return(1);
     break;
 
   case '4':
   case '5':
-    flow->ftp_imap_pop_smtp.auth_failed = 1;
+    flow->l4.tcp.ftp_imap_pop_smtp.auth_failed = 1;
     return(1);
     break;
   }
@@ -632,11 +632,11 @@ static void ndpi_check_ftp_control(struct ndpi_detection_module_struct *ndpi_str
 
 #ifdef FTP_DEBUG
 	printf("%s() [user: %s][pwd: %s]\n", __FUNCTION__,
-	       flow->ftp_imap_pop_smtp.username, flow->ftp_imap_pop_smtp.password);
+	       flow->l4.tcp.ftp_imap_pop_smtp.username, flow->l4.tcp.ftp_imap_pop_smtp.password);
 #endif
 
-	if(flow->ftp_imap_pop_smtp.password[0] == '\0' &&
-	   flow->ftp_imap_pop_smtp.auth_tls == 0) /* TODO: any values on dissecting TLS handshake? */
+	if(flow->l4.tcp.ftp_imap_pop_smtp.password[0] == '\0' &&
+	   flow->l4.tcp.ftp_imap_pop_smtp.auth_tls == 0) /* TODO: any values on dissecting TLS handshake? */
 	  flow->ftp_control_stage = 0;
 	else
 	  ndpi_int_ftp_control_add_connection(ndpi_struct, flow);