strongswan: add uci option for aggressive mode PSK

Add option 'aggressive' to the globals section of /etc/config/ipsec.
When enabled, the charon setting
'i_dont_care_about_security_and_use_aggressive_mode_psk = yes' is
written to the generated strongswan.conf. The setting is only
emitted when the option is active.

IKEv1 aggressive mode with PSK is sometimes required to interoperate
with old peers that do not support main mode with PSK.

If enabled, IKE Responders are allowed to use IKEv1 Aggressive Mode with
Pre-Shared Keys (PSKs). This is strongly discouraged due to security
concerns (offline attacks on the openly transmitted hash of the PSK).

Signed-off-by: Florian Eckert <fe@dev.tdt.de>

net/strongswan/files/swanctl.init

@@ -917,6 +917,16 @@ config_charon_common_install_routes() {
 	swan_xappend1 "install_routes = $install_routes"
 }
 
+config_charon_common_aggressive() {
+	local conf="$1"
+
+	local aggressive
+
+	config_get_bool aggressive "$conf" aggressive 0
+	[ $aggressive -eq 1 ] && \
+		swan_xappend1 "i_dont_care_about_security_and_use_aggressive_mode_psk = yes"
+}
+
 config_charon_common() {
 	local conf="$1"
 
@@ -924,6 +934,7 @@ config_charon_common() {
 	config_charon_common_interfaces_use "$conf"
 	config_charon_common_ignore_routing_tables "$conf"
 	config_charon_common_install_routes "$conf"
+	config_charon_common_aggressive "$conf"
 }
 
 config_strongswan_generate() {