ip: Support filter links with no VF info

ip: Support filter links with no VF info

Kernel has add IFLA_EXT_MASK attribute for indicating that certain
extended ifinfo values are requested by the user application. The ip
link show cmd always request VFs extended ifinfo.

In this case, RTM_GETLINK for greater than about 220 VFs truncates
IFLA_VFINFO_LIST due to the maximum reach of nlattr's nla_len being
exceeded. As a result, ip link show command only show the truncated
VFs info sucn as:

    #ip link show dev eth0
    1: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 ...
        link/ether ...
        vf 0     link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff ...
    Truncated VF list: eth0

This patch add novf to support filter links with no VF info:
ip link show novf

v2:
- use an one word option instead of an option with on/off.
- fix the issue that break changes made for the link filter
  already done for VF's.

v3:
- "novf" set vfinfo to 0 and the RTEXT_FILTER_VF flag is not added.

Signed-off-by: Mingshuai Ren <renmingshuai@huawei.com>
Reviewed-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David Ahern <dsahern@kernel.org>