MFC: 277885
MFC: 277885

sfxge: Move txq->next pointer to part writable on completion path

In fact the pointer is used only if more than one TXQ is processed in
one interrupt.
It is used (read-write) on completion path only.
Also it makes the first part of the structure smaller and it fits now
into one 128byte cache line. So, TXQ structure becomes 128 bytes
smaller.

Sponsored by:   Solarflare Communications, Inc.
Approved by:    gnn (mentor)

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase