smb: client: move rdma_readwrite_threshold from smbd_connection to TCP_Server_Info

smb: client: move rdma_readwrite_threshold from smbd_connection to TCP_Server_Info

This belongs to the SMB layer not to the transport layer, it
just uses the negotiated transport parameters to adjust the
value if needed.

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