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/patches/300-include-ipsec-hotplug.patch

@@ -0,0 +1,16 @@
+--- a/src/_updown/_updown.in
++++ b/src/_updown/_updown.in
+@@ -22,6 +22,13 @@
+ # that, and use the (left/right)updown parameters in ipsec.conf to make
+ # strongSwan use yours instead of this default one.
+ 
++# Add your custom commands to the file "/etc/ipsec.user". Other packages could
++# also install their scripts in the directory "/etc/hotplug.d/ipsec".
++# This files/scripts are executed by the openwrt hotplug functionality on
++# ipsec events.
++
++exec /sbin/hotplug-call ipsec "$1"
++
+ #      PLUTO_VERSION
+ #              indicates  what  version of this interface is being
+ #              used.  This document describes version  1.1.   This