infiniband: cxgb4: Consolidate 3 copies of the same operation into 1 helper function.

Three pieces of code do the same thing, create a l2t entry and then
import this information into the c4iw_ep object.

Create a helper function and call it from these 3 locations instead.

Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Roland Dreier <roland@purestorage.com>