b2b_entities: add more entropy to from_tag generation

The initial from-tag generation cosisted of an md5 hash over the From
URI. Thus, if you would have generating client requests to the same
entity (such as a media server), you would always get the same from-tag
for all those requests.
The current patch adds more entropy when generating the from_tag, such
as the current timestamp (expressed in milliseconds) along with the
process pid.

(cherry picked from commit b003891)

modules/b2b_entities/client.c

@@ -49,8 +49,20 @@ static char from_tag[FROM_TAG_LEN + 1];
 static void generate_tag(str* tag, str* src, str* callid)
 {
 	int len;
+	str srcs[4];
+	struct timeval tv;
 
-	MD5StringArray(from_tag, src, 1);
+	gettimeofday(&tv, NULL);
+
+	srcs[0] = *src;
+	srcs[1].s = (char *)&tv.tv_sec;
+	srcs[1].len = sizeof(tv.tv_sec);
+	srcs[2].s = (char *)&tv.tv_usec;
+	srcs[2].len = sizeof(tv.tv_usec);
+	srcs[3].s = (char *)&process_no;
+	srcs[3].len = sizeof(process_no);
+
+	MD5StringArray(from_tag, srcs, 4);
 	len = MD5_LEN;
 
 	/* calculate from tag from callid */