strongswan: write local_key to swanctl.conf

The 'local_key' UCI option was validated (checked for existence
under /etc/swanctl/private/) but never written to the generated
'swanctl.conf'. As a result, setting 'local_key' had no actual effect
on which private key was used for local authentication.

Add the corresponding "privkeys" line to the local{} section,
mirroring how local_cert is already written as "certs", so that
swanctl explicitly uses the configured private key.

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

net/strongswan/files/swanctl.init

@@ -553,6 +553,8 @@ config_remote() {
 	[ -n "$local_identifier" ] && swanctl_xappend3 "id = \"$local_identifier\""
 	[ "$local_auth_method" = pubkey ] && [ -n "$local_cert" ] && \
 		swanctl_xappend3 "certs = $local_cert"
+	[ "$local_auth_method" = pubkey ] && [ -n "$local_key" ] && \
+		swanctl_xappend3 "privkeys = $local_key"
 	swanctl_xappend2 "}"
 
 	swanctl_xappend2 "remote {"