[openswan] Fix ipsec restart

1. Restart ipsec in offload mode, if it was running
in offload mode, before network topology change.

2. Get the wan iface from uci instead of using eth0.

Signed-off-by: Neelansh Mittal <neelanshm@codeaurora.org>
Change-Id: Icdd71107af40928dd010e6df1cfd1baa9da8ee3a