Unlock the right lock.

The adist_remote_lock is not held in this place, whereas the
adist_recv_list_lock lock is and is picked up during the next iteration.

I found this by annotating our libpthread with Clang's -Wthread-safety
attributes. I will send out a patch for this in the nearby future,
because it's awesome.

MFC after:	2 weeks
Merge remote-tracking branch 'freebsd/master' into hardened/current/intel-smap