1. oce_multiq_start(): make sure the buffer is consumed even on ENXIO
2. oce_multiq_transmit(): there is an extra call to drbr_enqueue()
causing the mbuf to be enqueued twice when the NIC's queue is full,
and potential panics
3. oce_multiq_transmit(): same problem fixed recently in ixgbe (r267187)
and other drivers: if the mbuf is enqueued, the proper return value is 0
Submitted by: Stefano Garzarella
MFC after: 3 days
39ab708a85