interface: fix overflow of link speed.

interface: fix overflow of link speed.

Type: fix

There were several places where mbps were converted to kbps for
link_speed, but often drivers of devices set link speed to unknown
(0xFFFFFFFF) on initialization, so there was multiplication of
link_speed equal 0xFFFFFFFF(UINT32_MAX) by 1000, this provides
overflow of unsigned int, and as result link_speed was equal
4295 Gbps, but actually link_speed is unknown.

Signed-off-by: Anton Nikolaev <anikolaev@netgate.com>
Change-Id: Ib462ed6ed685654af4687041e115bfb74e640f13