Keep a STP port path cost value if it was set by a user.
Don't replace it with the link-speed based path cost
whenever the link goes down and comes back up.
Reported-by: NRoopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: NStephen Hemminger <stephen@networkplumber.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>