ike: Only track actually sent retransmits as outbound packets

ike: Only track actually sent retransmits as outbound packets

Retransmission jobs for old requests for which we already received a
response previously left the impression that messages were sent more
recently than was actually the case.

task_manager_t always defined INVALID_STATE as possible return value if
no retransmit was sent, this just was never actually returned.

I guess we could further differentiate between actual invalid states
(e.g. if we already received the response) and when we don't send a
retransmit for other reasons e.g. because the IKE_SA became stale.