RDMA: Simplify get firmware interface

There is a need to forward FW version to user space
application through RDMA netlink. In order to make it safe, there
is need to declare nla_policy and limit the size of FW string.

The new define IB_FW_VERSION_NAME_MAX will limit the size of
FW version string. That define was chosen to be equal to
ETHTOOL_FWVERS_LEN, because many drivers anyway are limited
by that value indirectly.

The introduction of this define allows us to remove the string size
from get_fw_str function signature.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
diff --git a/drivers/infiniband/hw/mlx4/main.c b/drivers/infiniband/hw/mlx4/main.c
index 1f25a37..c636842 100644
--- a/drivers/infiniband/hw/mlx4/main.c
+++ b/drivers/infiniband/hw/mlx4/main.c
@@ -2587,12 +2587,11 @@ static int mlx4_port_immutable(struct ib_device *ibdev, u8 port_num,
 	return 0;
 }
 
-static void get_fw_ver_str(struct ib_device *device, char *str,
-			   size_t str_len)
+static void get_fw_ver_str(struct ib_device *device, char *str)
 {
 	struct mlx4_ib_dev *dev =
 		container_of(device, struct mlx4_ib_dev, ib_dev);
-	snprintf(str, str_len, "%d.%d.%d",
+	snprintf(str, IB_FW_VERSION_NAME_MAX, "%d.%d.%d",
 		 (int) (dev->dev->caps.fw_ver >> 32),
 		 (int) (dev->dev->caps.fw_ver >> 16) & 0xffff,
 		 (int) dev->dev->caps.fw_ver & 0xffff);