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, 5 insertions, 5 deletions

diff --git a/src/lib/protocols/mail_imap.c b/src/lib/protocols/mail_imap.c
index 8a4e8fa2e..317ac1848 100644
--- a/src/lib/protocols/mail_imap.c
+++ b/src/lib/protocols/mail_imap.c
@@ -177,16 +177,16 @@ void ndpi_search_mail_imap_tcp(struct ndpi_detection_module_struct *ndpi_struct,
 	  if(user) {
 	    char *pwd;
 
-	    snprintf(flow->ftp_imap_pop_smtp.username,
-		     sizeof(flow->ftp_imap_pop_smtp.username),
+	    snprintf(flow->l4.tcp.ftp_imap_pop_smtp.username,
+		     sizeof(flow->l4.tcp.ftp_imap_pop_smtp.username),
 		     "%s", user);
 
 	    ndpi_set_risk(ndpi_struct, flow, NDPI_CLEAR_TEXT_CREDENTIALS);
 
 	    pwd = strtok_r(NULL, " \"\r\n", &saveptr);
 	    if(pwd) {
-	      snprintf(flow->ftp_imap_pop_smtp.password,
-	               sizeof(flow->ftp_imap_pop_smtp.password),
+	      snprintf(flow->l4.tcp.ftp_imap_pop_smtp.password,
+		       sizeof(flow->l4.tcp.ftp_imap_pop_smtp.password),
 	               "%s", pwd);
 	    }
 	  }
@@ -320,7 +320,7 @@ void ndpi_search_mail_imap_tcp(struct ndpi_detection_module_struct *ndpi_struct,
 	 || (flow->l4.tcp.mail_imap_stage == 5)
 	 || (flow->l4.tcp.mail_imap_stage == 7)
         ) {
-	if((flow->ftp_imap_pop_smtp.username[0] != '\0')
+	if((flow->l4.tcp.ftp_imap_pop_smtp.username[0] != '\0')
 	   || (flow->l4.tcp.mail_imap_stage >= 7)) {
 	  NDPI_LOG_INFO(ndpi_struct, "found MAIL_IMAP\n");
 	  ndpi_int_mail_imap_add_connection(ndpi_struct, flow);