Clear virtual IPs before storing assigned ones on the IKE_SA

Otherwise we'll end up with duplicate or invalid VIPs stored on the
IKE_SA.

src/libcharon/sa/ike_sa.h

@@ -941,6 +941,13 @@ struct ike_sa_t {
 	 */
 	void (*add_virtual_ip) (ike_sa_t *this, bool local, host_t *ip);
 
+	/**
+	 * Clear all virtual IPs stored on this IKE_SA.
+	 *
+	 * @param local			TRUE to clear local addresses, FALSE for remote
+	 */
+	void (*clear_virtual_ips) (ike_sa_t *this, bool local);
+
 	/**
 	 * Create an enumerator over virtual IPs.
 	 *