[packages] strongswan: add init script

Signed-off-by: Luka Logar <luka.logar@cifra.si>
Signed-off-by: Luka Perkov <luka@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/packages@36319 3c298f89-4303-0410-b956-a3cf2f4a3e73