nvmet: rename nvmet_check_data_len to nvmet_check_transfer_len

The function doesn't check only the data length, because the transfer
length includes also the metadata length in some cases. This is
preparation for adding metadata (T10-PI) support.

Signed-off-by: Israel Rukshin <israelr@mellanox.com>
Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>