net/mlx5: Properly name the generic WQE control field

A generic WQE control field is used for different purposes
in different cases.
Use union to allow using the proper name in each case.
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

include/linux/mlx5/qp.h

@@ -202,7 +202,12 @@ struct mlx5_wqe_ctrl_seg {
 	u8			signature;
 	u8			rsvd[2];
 	u8			fm_ce_se;
-	__be32			imm;
+	union {
+		__be32		general_id;
+		__be32		imm;
+		__be32		umr_mkey;
+		__be32		tisn;
+	};
 };
 
 #define MLX5_WQE_CTRL_DS_MASK 0x3f