Add an extended TIMOUTidle setting to stunnel

This change affects the client mode of stunnel only. An
equivalent for the server needs to be added elsewhere.

Signed-off-by: Jon Ludlam <jonathan.ludlam@eu.citrix.com>
Merge pull request #153 from zli/xenserver/sanibel-lcm/HFX-1147

HFX-1147
SCTX-1649: Set SO_KEEPALIVE on server sockets

This ensures that a TCP connection is cleaned up on the server, when the
connection is closed on the client without the server knowing (for example, if
a FIN packet is not sent or went missing).

This does not affect idle connections, or long-running XenAPI calls.

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>