cxgb4: Add MPS tracing support

Handle TRACE_PKT, stack can sniff them on the first port
Add debubfs enrty to configure tracing for offload traffic like iWARP
& iSCSI for debugging purpose.

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>