If, for any reason, the open-coded arithmetic causes a wraparound,
the protection that `struct_size()` provides against potential integer
overflows is defeated. Fix this by hardening calls to `struct_size()`
with `size_add()`, `size_sub()` and `size_mul()`.

Fixes: 467f432a ("RDMA/core: Split port and device counter sysfs attributes")
Fixes: a4676388 ("RDMA/core: Simplify how the gid_attrs sysfs is created")
Fixes: e9dd5daf ("IB/umad: Refactor code to use cdev_device_add()")
Fixes: 324e227e ("RDMA/device: Add ib_device_get_by_netdev()")
Fixes: 5aad26a7 ("IB/core: Use struct_size() in kzalloc()")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/ZQdt4NsJFwwOYxUR@workSigned-off-by: Leon Romanovsky <leon@kernel.org>