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/hw/i40iw/i40iw_verbs.c

@@ -2584,13 +2584,12 @@ static const char * const i40iw_hw_stat_names[] = {
 		"iwRdmaInv"
 };
 
-static void i40iw_get_dev_fw_str(struct ib_device *dev, char *str,
-				 size_t str_len)
+static void i40iw_get_dev_fw_str(struct ib_device *dev, char *str)
 {
 	u32 firmware_version = I40IW_FW_VERSION;
 
-	snprintf(str, str_len, "%u.%u", firmware_version,
-		       (firmware_version & 0x000000ff));
+	snprintf(str, IB_FW_VERSION_NAME_MAX, "%u.%u", firmware_version,
+		 (firmware_version & 0x000000ff));
 }
 
 /**