docs: networking: Replace strncpy() with strscpy()

Replace example code's use of strncpy() with strscpy() functions. Using
strncpy() is considered deprecated:
https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Link: https://lore.kernel.org/r/20210602202914.4079123-1-keescook@chromium.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/input/joydev/joystick-api.rst

@@ -263,7 +263,7 @@ possible overrun should the name be too long::
 
 	char name[128];
 	if (ioctl(fd, JSIOCGNAME(sizeof(name)), name) < 0)
-		strncpy(name, "Unknown", sizeof(name));
+		strscpy(name, "Unknown", sizeof(name));
 	printf("Name: %s\n", name);