cxgbe/t4_tom: add a knob to the default configuration file to tune
the TOE for LAN operation. It is possible to set this to other values
(cluster for networks with little loss and really tight RTTs, and wan
for relatively large RTTs and/or lossy networks) depending on the
environment in which the TOE is being used.

None of this affects plain NIC operation in any way.

MFC after: 1 week