Sanity-check CSTP and DTLS rekey times

Just set REKEY_NONE if the rekey time is zero or negative, so that we
don't need to test (ka->rekey && ka->rekey_method != REKEY_NONE) in
multiple locations.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

cstp.c

@@ -509,6 +509,9 @@ static int start_cstp_connection(struct openconnect_info *vpninfo)
 	if (!sessid_found)
 		vpninfo->dtls_attempt_period = 0;
 
+	if (vpninfo->ssl_times.rekey <= 0)
+		vpninfo->ssl_times.rekey_method = REKEY_NONE;
+
 	vpninfo->ssl_times.last_rekey = vpninfo->ssl_times.last_rx =
 		vpninfo->ssl_times.last_tx = time(NULL);
 	return 0;

dtls.c

@@ -622,6 +622,8 @@ int openconnect_setup_dtls(struct openconnect_info *vpninfo, int dtls_attempt_pe
 		vpninfo->dtls_attempt_period = 0;
 		return -EINVAL;
 	}
+	if (vpninfo->dtls_times.rekey <= 0)
+		vpninfo->dtls_times.rekey_method = REKEY_NONE;
 
 	vpninfo->dtls_addr = malloc(vpninfo->peer_addrlen);
 	if (!vpninfo->dtls_addr) {