- Change the wakeup logic associated with having multiple sleepers

on multiple different audit pipes.  The old method used cv_signal()
  which would result in only one thread being woken up after we
  appended a record to it's queue.  This resulted in un-timely wake-ups
  when processing audit records real-time.

- Assign PSOCK priority to threads that have been sleeping on a read(2).
  This is the same priority threads are woken up with when they select(2)
  or poll(2).  This yields fairness between various forms of sleep on
  the audit pipes.

Obtained from:	TrustedBSD Project
Discussed with:	rwatson
MFC after:	1 week

sys/security/audit/audit_pipe.c

@@ -466,7 +466,7 @@ audit_pipe_submit(au_id_t auid, au_event_t event, au_class_t class, int sorf,
 	}
 	audit_pipe_records++;
 	mtx_unlock(&audit_pipe_mtx);
-	cv_signal(&audit_pipe_cv);
+	cv_broadcastpri(&audit_pipe_cv, PSOCK);
 }
 
 /*
@@ -493,7 +493,7 @@ audit_pipe_submit_user(void *record, u_int record_len)
 		audit_pipe_append(ap, record, record_len);
 	audit_pipe_records++;
 	mtx_unlock(&audit_pipe_mtx);
-	cv_signal(&audit_pipe_cv);
+	cv_broadcastpri(&audit_pipe_cv, PSOCK);
 }