kernel - Fix a third missing wakeup() in kern_lock.c

kernel - Fix a third missing wakeup() in kern_lock.c

* Fix a case where an lockmgr LK_EXCLUSIVE call with a
  timeout blocks due to existing shared locks.  If the
  timeout occurs, the exclusive lock request is backed out.

  However, if any new shared locks are attempted while
  the EXREQ was pending (due to the exclusive priority
  mechanism), those threads will block.  The backout code
  was not waking the blocked threads up for this situation.

* Fixed by issuing the wakeup() unconditionally for this
  case.  This is not a heavily traveled code path as locks
  with timeouts rarely reach the actual timeout.