smb: server: make use of smbdirect_connection_recv_io_refill[_work]()

smb: server: make use of smbdirect_connection_recv_io_refill[_work]()

This is basically a copy of smb_direct_post_recv_credits(), but
there are several improvements compared to the existing function:

1. We calculate the number of missing posted buffers by getting the
   difference between recv_io.credits.target and recv_io.posted.count.

   Instead of the difference between recv_io.credits.target
   and recv_io.credits.count, because recv_io.credits.count is
   only updated once a message is send to the peer.

   It was not really a problem before, because we have
   a fixed number smbdirect_recv_io buffers, so the
   loop terminated when smbdirect_connection_get_recv_io()
   returns NULL.

   But using recv_io.posted.count makes it easier to
   understand.

2. In order to tell the peer about the newly posted buffer
   and grant the credits, we only trigger the send immediate
   when we're not granting only the last possible credit.

   This is mostly a difference relative to the servers
   smb_direct_post_recv_credits() implementation,
   which should avoid useless ping pong messages.

Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>