cifs: smbd: Don't use RDMA read/write when signing is used

cifs: smbd: Don't use RDMA read/write when signing is used

SMB server will not sign data transferred through RDMA read/write. When
signing is used, it's a good idea to have all the data signed.

In this case, use RDMA send/recv for all data transfers. This will degrade
performance as this is not generally configured in RDMA environemnt. So
warn the user on signing and RDMA send/recv.

Signed-off-by: Long Li <[email protected]>
Acked-by: Ronnie Sahlberg <[email protected]>
Cc: [email protected]
Signed-off-by: Steve French <[email protected]>