net/smc: add v2 support to the work request layer

In the work request layer define one large v2 buffer for each link group
that is used to transmit and receive large LLC control messages.
Add the completion queue handling for this buffer.

Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>