xprtrdma: Replace outdated comment for rpcrdma_ep_post

Since commit 7c8d9e7c ("xprtrdma: Move Receive posting to
Receive handler"), rpcrdma_ep_post is no longer responsible for
posting Receive buffers. Update the documenting comment to reflect
this change.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/verbs.c

@@ -1427,10 +1427,14 @@ rpcrdma_free_regbuf(struct rpcrdma_regbuf *rb)
 	kfree(rb);
 }
 
-/*
- * Prepost any receive buffer, then post send.
+/**
+ * rpcrdma_ep_post - Post WRs to a transport's Send Queue
+ * @ia: transport's device information
+ * @ep: transport's RDMA endpoint information
+ * @req: rpcrdma_req containing the Send WR to post
  *
- * Receive buffer is donated to hardware, reclaimed upon recv completion.
+ * Returns 0 if the post was successful, otherwise -ENOTCONN
+ * is returned.
  */
 int
 rpcrdma_ep_post(struct rpcrdma_ia *ia,