unity: Handle narrowing according to roles in the IKE_SA

Since the narrow hook types reflect the roles in the Quick Mode exchange
the plugin behaved incorrectly if the server initiated the CHILD_SA
rekeying.
unity: Do not bump TS to 0.0.0.0/0 as initiator when no Split-Include received

When having the unity plugin enabled and both peers send the Unity Vendor ID,
we proposed 0.0.0.0/0 as traffic selector, even if no Split-Include has been
received on the SA. This can break compatibility with some responders, as
they don't narrow the TS themselves, but expect the configured TS.