davidcs d572331020 - Avoid lock contention in the if_transmit callback by using trylock and
enqueueing the frames when it fails. This way there is some latency
 removed from the transmitting path.
- If IFF_DRV_OACTIVE is set (and also if IFF_DRV_RUNNING is not) just
 enqueue the desired frames and return successful transmit. This way we
 avoid to return errors on transmit side and resulting in
 possible out-of-order frames. Please note that IFF_DRV_OACTIVE is set
 everytime we get the threshold ring hit, so this can be happening quite
 often.

Submitted by:	Attilio.Rao@isilon.com
MFC after:5 days
2015-07-28 19:15:44 +00:00
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