net/i40e: set speed to undefined for default case

net/i40e: set speed to undefined for default case

During PF/VF link update, a default speed value of 100M will be set
if get_link_info has failed or speed is unknown.

Consequently if PF is put in no-carrier state, VFs will switch to
"in carrier" state due to a link up + a link speed set to 100M
(default value if no speed detected).

To be consistent with linux drivers on which PF and VFs are in
same carrier state, sets default speed to undefined (instead of 100M)
and updates a link status of VF only if link is up and speed is
different from undefined.

Fixes: 4861cde46116 ("i40e: new poll mode driver")
Cc: stable@dpdk.org
Signed-off-by: Laurent Hardy <laurent.hardy@6wind.com>
Reviewed-by: Xiaolong Ye <xiaolong.ye@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>