RDMA/nes: Add wqm_quanta module option

Add a module parameter wqm_quanta.  It controls the number of segments
transmitted at a time.

Signed-off-by: Sweta Bhatt <sweta.bhatt@einfochips.com>
Signed-off-by: Chien Tung <ctung@neteffect.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>