Starting with re1 NOT plugged:

root@fbsd-router:~ # dtrace -s bridge.d

=> Now I plug re1:

dtrace: script 'bridge.d' matched 3 probes
CPU     ID                    FUNCTION:NAME
  1  16563       do_link_state_change:entry
              kernel`taskqueue_run_locked+0x13b
              kernel`taskqueue_run+0xaf
              kernel`intr_event_execute_handlers+0x1b6
              kernel`ithread_loop+0xa6
              kernel`fork_exit+0x9c
              kernel`0xffffffff80f0dc3e
linkstate for bridge0: UP -> DOWN

=> Now I unplug re1:

  1  16563       do_link_state_change:entry
              kernel`taskqueue_run_locked+0x13b
              kernel`taskqueue_run+0xaf
              kernel`intr_event_execute_handlers+0x1b6
              kernel`ithread_loop+0xa6
              kernel`fork_exit+0x9c
              kernel`0xffffffff80f0dc3e
linkstate for bridge0: DOWN -> DOWN

=> Now I replug re1:

  1  16563       do_link_state_change:entry
              kernel`taskqueue_run_locked+0x13b
              kernel`taskqueue_run+0xaf
              kernel`intr_event_execute_handlers+0x1b6
              kernel`ithread_loop+0xa6
              kernel`fork_exit+0x9c
              kernel`0xffffffff80f0dc3e
linkstate for bridge0: UP -> DOWN