Avoids lock recursion in rndsinks:
rndsink user holds lock
calls rndsink_request
calls rnd_getmore
calls an rndsource callback
calls rnd_add_data
calls rnd_process_events
calls rndsinks_distribute
calls rndsink callback
acquires rndsink user lock.
This can happen only before the rnd_process_events softint is
established, but that's enough to cause a problem and is the main
reason why all our HWRNG drivers are so byzantine (soon to be
fixed!).
ok tls
3945f2f07a