RDMA/core: introduce check masks for T10-PI offload

T10-PI offload capability is currently supported in iSER protocol only,
and the definition of the HCA protection information checks are missing
from the core layer. Add those definition to avoid code duplication in
other drivers (such iSER target and NVMeoF).

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

include/rdma/ib_verbs.h

@@ -860,6 +860,19 @@ enum ib_sig_err_type {
 	IB_SIG_BAD_APPTAG,
 };
 
+/**
+ * Signature check masks (8 bytes in total) according to the T10-PI standard:
+ *  -------- -------- ------------
+ * | GUARD  | APPTAG |   REFTAG   |
+ * |  2B    |  2B    |    4B      |
+ *  -------- -------- ------------
+ */
+enum {
+	IB_SIG_CHECK_GUARD	= 0xc0,
+	IB_SIG_CHECK_APPTAG	= 0x30,
+	IB_SIG_CHECK_REFTAG	= 0x0f,
+};
+
 /**
  * struct ib_sig_err - signature error descriptor
  */