Fix setting of IP addresses in ip_info from PPP

We were clearing vpninfo->ip_info.addr if it was already set, as shown in
adrienverge/openfortivpn#112 (comment)

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

ppp.c

@@ -947,16 +947,12 @@ static int handle_state_transition(struct openconnect_info *vpninfo, int dtls,
 		if (ppp->want_ipv4 && !vpninfo->ip_info.addr) {
 			vpninfo->ip_info.addr = add_option_ipaddr(&vpninfo->cstp_options, "ppp_ipv4",
 								  AF_INET, &ppp->out_ipv4_addr);
-		} else {
-			vpninfo->ip_info.addr = NULL;
 		}
 
 		/* Ensure that we use the addresses we configured on PPP */
 		if (ppp->want_ipv6 && !vpninfo->ip_info.addr6 && !vpninfo->ip_info.netmask6) {
 			vpninfo->ip_info.addr6 = add_option_ipaddr(&vpninfo->cstp_options, "ppp_ipv6",
 								   AF_INET6, &ppp->out_ipv6_addr);
-		} else {
-			vpninfo->ip_info.addr6 = NULL;
 		}
 
 		if (ppp->got_peerns & IPCP_NBNS0)