Call em_start() when we detect a link state change such that packets start flowing again even if the send queue is currently full.  Restores the fix made by makeb@ in rev 1.263 which was lost in making the tx completion path mpsafe.
Call em_start() when we detect a link state change such that packets start
flowing again even if the send queue is currently full.  Restores the fix
made by makeb@ in rev 1.263 which was lost in making the tx completion path
mpsafe.

ok mikeb@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars