xprtrdma: Refactor initialization of ep->rep_max_requests

Clean up: there is no need to keep two copies of the same value.
Also, in subsequent patches, rpcrdma_ep_create() will be called in
the connect worker rather than at set-up time.

Minor fix: Initialize the transport's sendctx to the value based on
the capabilities of the underlying device, not the maximum setting.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>