if leftsourceip is defined, it is requested.
server may define rightsourceip=%config to accept any,
or it may overwrite it using rightsourceip.
if server does not return an IP, client enforces its configured leftsourceip.
new configuration structure:
peer_cfg: configuration related to a peer (authenitcation, ...=
ike_cfg: config to use for IKE setup (proposals)
child_Cfg: config for CHILD_SA (proposals, traffic selectors)
a peer_cfg has one ike_cfg and multiple child_cfg's
stroke now uses fixed count of threads
Martin Willi