igbvf: replace deprecated strncpy with strscpy

igbvf: replace deprecated strncpy with strscpy

`strncpy` is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect netdev->name to be NUL-terminated based on its usage with
`strlen` and format strings:
|       if (strlen(netdev->name) < (IFNAMSIZ - 5)) {
|               sprintf(adapter->tx_ring->name, "%s-tx-0", netdev->name);

Moreover, we do not need NUL-padding as netdev is already
zero-allocated:
|       netdev = alloc_etherdev(sizeof(struct igbvf_adapter));
...
alloc_etherdev() -> alloc_etherdev_mq() -> alloc_etherdev_mqs() ->
alloc_netdev_mqs() ...
|       p = kvzalloc(alloc_size, GFP_KERNEL_ACCOUNT | __GFP_RETRY_MAYFAIL);

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Link: https://github.com/KSPP/linux/issues/90
Signed-off-by: Justin Stitt <justinstitt@google.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20231017190411.2199743-9-jacob.e.keller@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>