xhttp: use proper function to set the ip addres of the fake via

- for ipv6 it has to be enclosed in between [ ]
- reported by Sergey Okhapkin

(cherry picked from commit 5c1a9df)

modules/xhttp/xhttp_mod.c

@@ -199,7 +199,7 @@ static char* xhttp_to_sip(sip_msg_t* msg, int* new_msg_len)
 	struct hostport hp;
 	struct dest_info dst;
 
-	ip.s = ip_addr2a(&msg->rcv.src_ip);
+	ip.s = ip_addr2strz(&msg->rcv.src_ip);
 	ip.len = strlen(ip.s);
 	port.s = int2str(msg->rcv.src_port, &port.len);
 	hp.host = &ip;