setting MTU breaks receive

[acooks]

Setting the MTU intermittently causes the NIC to stop receiving frames. The MTU value being set does not matter - valid and invalid values will have the same effect.

Bug found using net-driver-test .

Defect Affects:
release/tn40xx-005 and release/tn40xx-006 (and probably earlier versions too)

Edit: Seems to be intermittent. Need info.