rtnetlink: reject non-IFLA_VF_PORT attributes inside IFLA_VF_PORTS

Similarly as in commit 4f7d2cdf ("rtnetlink: verify IFLA_VF_INFO
attributes before passing them to driver"), we have a double nesting
of netlink attributes, i.e. IFLA_VF_PORTS only contains IFLA_VF_PORT
that is nested itself. While IFLA_VF_PORTS is a verified attribute
from ifla_policy[], we only check if the IFLA_VF_PORTS container has
IFLA_VF_PORT attributes and then pass the attribute's content itself
via nla_parse_nested(). It would be more correct to reject inner types
other than IFLA_VF_PORT instead of continuing parsing and also similarly
as in commit 4f7d2cdf, to check for a minimum of NLA_HDRLEN.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Roopa Prabhu <roopa@cumulusnetworks.com>
Cc: Scott Feldman <sfeldma@gmail.com>
Cc: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>