bnxt_en: Fix VF virtual link state.

If the physical link is down and the VF virtual link is set to "enable",
the current code does not always work.  If the link is down but the
cable is attached, the firmware returns LINK_SIGNAL instead of
NO_LINK.  The current code is treating LINK_SIGNAL as link up.
The fix is to treat link as down when the link_status != LINK.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>