netlink: bug fix: wrong size was calculated for vfinfo list blob

The wrong size was being calculated for vfinfo.  In one case, it was over-
calculating using nlmsg_total_size on attrs, in another case, it was
under-calculating by assuming ifla_vf_* structs are packed together, but
each struct is it's own attr w/ hdr (and padding).

Signed-off-by: Scott Feldman <scofeldm@cisco.com>
Signed-off-by: David S. Miller <davem@davemloft.net>