net/rds: Replace deprecated strncpy() with strscpy_pad()

strncpy() is deprecated for NUL-terminated destination buffers. Use
strscpy_pad() instead and remove the manual NUL-termination.

Compile-tested only.

Link: https://github.com/KSPP/linux/issues/90


Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Reviewed-by: Kees Cook <kees@kernel.org>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Tested-by: Allison Henderson <allison.henderson@oracle.com>
Link: https://patch.msgid.link/20250219224730.73093-2-thorsten.blum@linux.dev


Signed-off-by: Jakub Kicinski <kuba@kernel.org>