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>

drivers/infiniband/ulp/ipoib/ipoib_ethtool.c

@@ -62,8 +62,7 @@ static void ipoib_get_drvinfo(struct net_device *netdev,
 {
 	struct ipoib_dev_priv *priv = ipoib_priv(netdev);
 
-	ib_get_device_fw_str(priv->ca, drvinfo->fw_version,
-			     sizeof(drvinfo->fw_version));
+	ib_get_device_fw_str(priv->ca, drvinfo->fw_version);
 
 	strlcpy(drvinfo->bus_info, dev_name(priv->ca->dev.parent),
 		sizeof(drvinfo->bus_info));