strongswan: add openwrt hotplug script handling

Ipsec user script (/etc/ipsec.user) now get called indirectly by openwrt
"/sbin/hotplug-call". So other packages could also install their scripts
in "/etc/hotplug.d/ipsec".

Signed-off-by: Florian Eckert <fe@dev.tdt.de>
(cherry picked from commit 6cd8fcabe6)

net/strongswan/files/etc/hotplug.d/ipsec/01-user

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+[ -e "/etc/ipsec.user" ] && {
+	. /etc/ipsec.user "$2"
+}
+
+exit 0