If we fail connecting to the host we got redirected to, we should restart
with the original host where we might get redirected to a different host.
We must not reset this when retrying due to INVALID_KE_PAYLOAD or COOKIE
notifies. Since we keep the initiator SPI in those cases, we use that
flag as indicator.
Since we don't store the original remote_host value, we can't restore
that. So there is a potential conflict with MIPv6.
Closesstrongswan/strongswan#171.