add interface name validation

[mars1024]

Interface name in linux is not unrestricted, so bad interface name will break CNI plugin.
This pr will add interface name validation to libcni and skel.

validation rules ref to https://github.com/torvalds/linux/blob/master/net/core/dev.c#L1024

[mars1024]

@jellonek all updated, ptal, thanks ~

[jellonek]

lgtm

[dcbw]

For reference, from net/core/dev.c:

/**
 *	dev_valid_name - check if name is okay for network device
 *	@name: name string
 *
 *	Network device names need to be valid file names to
 *	to allow sysfs to work.  We also disallow any kind of
 *	whitespace.
 */
bool dev_valid_name(const char *name)
{
	if (*name == '\0')
		return false;
	if (strnlen(name, IFNAMSIZ) == IFNAMSIZ)
		return false;
	if (!strcmp(name, ".") || !strcmp(name, ".."))
		return false;

	while (*name) {
		if (*name == '/' || *name == ':' || isspace(*name))
			return false;
		name++;
	}
	return true;
}

[squeed]

Aha, interesting. @mars1024 can you block "." and ".." too?

[jellonek]

If we want to follow this kernel code - we should also block ":".

[mars1024]

@dcbw @squeed @jellonek Thanks for all your suggestions, I'll update this soon ~

[mars1024]

Updated!

[jellonek]

LGTM