RDMA/IPoIB: Fix format truncation compilation errors

Truncate the device name to store IPoIB VLAN name.

[leonro@5b4e8fba4ddd kernel]$ make -s -j 20 allmodconfig
[leonro@5b4e8fba4ddd kernel]$ make -s -j 20 W=1 drivers/infiniband/ulp/ipoib/
drivers/infiniband/ulp/ipoib/ipoib_vlan.c: In function ‘ipoib_vlan_add’:
drivers/infiniband/ulp/ipoib/ipoib_vlan.c:187:52: error: ‘%04x’
directive output may be truncated writing 4 bytes into a region of size
between 0 and 15 [-Werror=format-truncation=]
  187 |         snprintf(intf_name, sizeof(intf_name), "%s.%04x",
      |                                                    ^~~~
drivers/infiniband/ulp/ipoib/ipoib_vlan.c:187:48: note: directive
argument in the range [0, 65535]
  187 |         snprintf(intf_name, sizeof(intf_name), "%s.%04x",
      |                                                ^~~~~~~~~
drivers/infiniband/ulp/ipoib/ipoib_vlan.c:187:9: note: ‘snprintf’ output
between 6 and 21 bytes into a destination of size 16
  187 |         snprintf(intf_name, sizeof(intf_name), "%s.%04x",
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  188 |                  ppriv->dev->name, pkey);
      |                  ~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[6]: *** [scripts/Makefile.build:244: drivers/infiniband/ulp/ipoib/ipoib_vlan.o] Error 1
make[6]: *** Waiting for unfinished jobs....

Fixes: 9baa0b0 ("IB/ipoib: Add rtnl_link_ops support")
Link: https://lore.kernel.org/r/e9d3e1fef69df4c9beaf402cc3ac342bad680791.1715240029.git.leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>

Author: rleon

drivers/infiniband/ulp/ipoib/ipoib_vlan.c

@@ -184,8 +184,12 @@ int ipoib_vlan_add(struct net_device *pdev, unsigned short pkey)
 
 	ppriv = ipoib_priv(pdev);
 
-	snprintf(intf_name, sizeof(intf_name), "%s.%04x",
-		 ppriv->dev->name, pkey);
+	/* If you increase IFNAMSIZ, update snprintf below
+	 * to allow longer names.
+	 */
+	BUILD_BUG_ON(IFNAMSIZ != 16);
+	snprintf(intf_name, sizeof(intf_name), "%.10s.%04x", ppriv->dev->name,
+		 pkey);
 
 	ndev = ipoib_intf_alloc(ppriv->ca, ppriv->port, intf_name);
 	if (IS_ERR(ndev)) {