When the adist_free list is empty and we lose connection to the receiver we
move all elements from the adist_send and adist_recv lists back onto the
adist_free list, but we don't wake consumers waitings for the adist_free list
to become non-empty. This can lead to the sender process stopping audit trail
files distribution and waiting forever.

Fix the problem by adding the missing wakeup.

While here slow down spinning on CPU in case of a short race in
sender_disconnect() and add an explaination when it can occur.

PR: 201953
Reported by: peter
Approved by: re (kib)