igc: replace deprecated strncpy with strscpy

igc: 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 use with format
strings:
|       if (q_vector->rx.ring && q_vector->tx.ring)
|               sprintf(q_vector->name, "%s-TxRx-%u", netdev->name,

Furthermore, we do not need NUL-padding as netdev is already
zero-allocated:
|       netdev = alloc_etherdev_mq(sizeof(struct igc_adapter),
|                                  IGC_MAX_TX_QUEUES);
...
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/20231017190411.2199743-10-jacob.e.keller@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>